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Biotechnology and its Applications class 12 Notes Biology

Biotechnology deals with industrial-scale production of bio pharmaceuticals and biological using genetically modified microbes, fungi, plants and animals. It application includes therapeutics, diagnostics, genetically modified crops for agriculture, processed food, bio remediation, waste treatment and energy production. The main three critical research areas of biotechnology includes –

1. Providing the best catalyst in the form of improved organism usually a microbes or pure enzyme.
2. Creating optimal conditions through engineering for a catalyst to act.
3. Downstream processing technologies to purify the protein or organic compounds.

Biotechnological Applications in Agriculture- food production can be increased by

a) Agro-chemical based agriculture

b) Organic agriculture

c) Genetically engineered crop-based agriculture.

• Green revolution successfully increased the food production many folds by using better management practices and use of agrochemicals, fertilizers and pesticides. Further increase in production is not possible by using these methods. To overcome this genetically modified crop is used.
• Plants, bacteria, fungi and animals whose genes have been altered by manipulation are called Genetically Modified Organisms (GMO). GM plants have many applications-
• Made crops more tolerant to abiotic stresses
• Reduced reliance on chemical pesticides
• Helped to reduce post harvest losses
• Increased efficiency of mineral usage by plants
• Enhanced nutritional value of food, eg., Vitamin ‘A’ enriched rice.

Application of Biotechnology in production of pest-resistant plants–

Pest resistant plants decrease the amount of pesticides used. Bt toxin is produced by a bacterium called Bacillus thuringiensis.Bt toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for insecticides; in effect created a bio-pesticide. Examples are Bt cotton, Bt corn, rice, tomato, potato and soyabean etc

Bt cotton– Bacterium Bacillus thuringiensis produce proteins that kill certain insects like lepidopterens, colepterans (beetels) and dipterans (flies, mosquitoes).

• B. thuringiensisproduce crystals that contain a toxic insecticidal protein. This toxic protein present in bacterium as inactive protoxins but as soon as insect ingest the inactive form due to alkaline pH of gut, it converted into an active form of toxin and bind to surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually death of insect.
• The gene from B. thuringiensishas been incorporated into several crop plants like cotton, maize, rice etc. The toxin is coded by a gene named cry. The protein coded by the genes crylAb and cryIIAb control the cotton bollworms, cryIAb controls corn borer.

Pest Resistant Plants

• Nematodes like Meloidegyne incognitia infects the roots of tobacco plants and causes reduction in yield. The infestation of these nematodes can be prevented by the process of RNA interference (RNAi). RNAi is present in all eukaryotic organisms as cellular defence by silencing of specific mRNA due to complementary dsRNA molecules that bind to and prevents translation of the mRNA.
  
• The source of complementary dsRNA may be from an infection by viruses having RNA genomes or mobile genetic elements that replicate through RNA intermediate.
• Nematode specific genes were introduced into host plant using Agrobacterium vectors. The parasite could not survive in a transgenic host expressing specific interfering RNA.

Biotechnological Applications in Medicine

The rDNA technological processes have made immense impact in the area of healthcare by enabling mass production of safe and more effective therapeutic drugs.  At present, about 30 recombinant therapeutics have been approved for human use the world over. In India, 12 of these are presently being marketed.

Genetically Engineered Insulin

Adult –onset diabetes can be controlled by taking insulin at regular intervals. The main source of this insulin was isolation of insulin from animals. Now a day’s insulin can be obtained from bacterium using techniques of biotechnology.

• Insulin was earlier extracted from pancreas of slaughtered cattle and pigs but insulin from these sources develops allergy or other types of reactions to the foreign protein.
• Insulin consists of two short polypeptide chains- chain A and chain B, that are linked together by disulphide bridges.

• In humans, insulin is synthesised as a prohormone, which contains an extra stretch called C peptide, which is absent in mature insulin. The main challenge for production of insulin using rDNA technique was getting insulin assembled into a mature form.
• An American company, Eli Lilly in 1983 prepared two DNA sequence corresponding to A and B chain of human insulin and introduced them in plasmids of E.coli to produce insulin chain. Chain A and Chain B were produced separately, extracted and combined by creating disulphide bonds to form human insulin.

Gene Therapy

It is a collection of methods that allows correction of a gene defect that has been diagnosed in a child or embryo. This method is applied in a person with a hereditary disease. In this method, genes are inserted into a person’s cells and tissues to treat a disease.

• The correction of gene defect involves delivery of a normal gene into the individual or embryo to take over the function of and compensate for non-functional gene.
• The first clinical gene therapy was done in 1990 to a 4 year old girl with adenosine deaminase (ADA) deficiency. This disorder is caused due to the deletion of the gene for adenosine deaminase that is essential for immune system to function. This defect can be treated by enzyme replacement therapy in which functional ADA is given to the patient by injection or bone marrow transplant.
• In gene therapy method lymphocytes from the blood of the patient are grown in culture medium outside the body. A functional ADA cDNA is then introduced into these lymphocystes and returned to the patient. In this method periodic infusion of such genetically engineered lymphocytes is needed. If gene isolated from bone marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.

Molecular Diagnosis

Conventional method of diagnosis such as serum or urine analysis is not able to early detection of disease causing pathogens or virus. Following methods can be used to diagnosed earlier-

I. Recombinant DNA technology

II. Polymerase Chain Reaction (PCR)

III. Enzyme Linked Immuno-sorbent Assay (ELISA).

• Symptoms of disease appear only when the concentration of pathogen get increased significantly. Low concentration of bacteria and virus can be detected by amplification of nucleic acid by PCR. It detects the mutation in the gene in cancer patient. PCR is routinely used to detect the HIV in suspected AIDS patients. Genetic disorder can be also detected by using PCR technique.
• A single stranded DNA or RNA having radioactive molecule is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography. The clone having the mutated gene will not appear on the photographic film.
• ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens like proteins, glycoproteins etc. or by detecting the antibodies synthesised against the pathogen.

Transgenic Animals

Animals that have had their DNA manipulated to possess and express a foreign gene are known as transgenic animals. Transgenic mice, rats, rabbits, pigs, sheep, cows and fish have been produced. Common reasons for development of transgenic animals-

a) Normal physiology and development– they are designed to allow the study of gene regulation, their effect on normal function of body. By introducing genes from other species that alter the formation of this factor and studying eh biological affects that results.

b) Study of disease– a number of transgenic animals are designed to increase our understanding of how genes contribute to the development of disease. Transgenic model has been developed for disease like cancer, cystic fibrosis, Alzheimer’s disease etc.

c) Biological products– .Transgenic animals that produce useful biological products can be created by the introduction of the portion of DNA (gene) which codes for a particular product such as human protein (alpha – 1-antitrypsin) used to treat emphysema.  The first transgenic cow, Rosie, produced human protein-enriched milk (alpha-lactalbumin – 2.4 gm / litre).

d) Vaccine safety– transgenic mice are developed for used in testing the safety of vaccine before they are used on human. Polio vaccine was tested on transgenic mice and then on monkey.

e) Chemical safety testing– transgenic animals are made that carry genes which make them more sensitive to toxic substances than non-transgenic animals. It gives us the results in less time.

Ethical Issues:

The Indian Government has set up organizations such as GEAC (Genetic Engineering Approval Committee), which will make decisions regarding the validity of GM research and the safety of introducing GM-organisms for public services.Biopatent:
A patent is the right granted by a government to an inventor to prevent others from making commercial use of his invention. Now, patents are granted for biological entities and for products derived from biological resources.Biopiracy:
It is the term used to refer to the use of bio-resources by multinational companies and other organizations without proper authorization from the countries and people concerned without compensatory payment.

In 1997, an American company got patent rights on Basmati rice through the US Patent and Trademark Office.  This allowed the company to sell a ‘new variety of Basmati, in the US and abroad.  This ‘new’ variety of Basmati had actually been derived from Indian farmer’s varieties. Indian Basmati was crossed with semi-dwarf varieties and claimed as an invention or a novelty.

Several attempts have also been made to patent uses, products and processes based on Indian traditional herbal medicines, e.g., turmeric and neem.   

 Biology Revision Notes Chapter 11 Biotechnology Principles and Processes

The techniques of using live organisms or enzymes from organisms to produce products and processes useful to humans. Many processes like in vitro fertilization leading to ‘test-tube’ baby, synthesizing gene and using it, developing a DNA vaccine or correcting a defective gene are also parts of Biotechnology.

The European Federation of Biotechnology (EFB) has given a definition of biotechnology that comprises both traditional and modern molecular biotechnology.The definition is as follow- “The integration of natural science and organisms, cells, parts thereof, and molecular analogous for products and services”.

Principles of Biotechnology

Modern biotechnology is based on two main principles-

• Genetic Engineering – Genetic Engineering is defined as the direct manipulation of genome (DNA and RNA) of an organism. It involves the transfer of new genes to improve the function or trait into host organisms and thus changes the phenotype of the host organism.

• Maintenance of sterile condition in chemical engineering process to enable growth of only desired microbes for manufacture of biotechnological products like antibiotics, vaccine, enzymes etc.

• Traditional hybridization used in plants and animal breeding leads to inclusion and multiplication of undesirable genes along with the desired traits. The technique of genetic engineering which include creation of recombinant DNA, use of gene cloning and gene transfer allow us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism.

• In a chromosome there is a specific DNA sequence called the origin of replication, which is responsible for initiating replication. Therefore, for the multiplication of any alien piece of DNA in an organism, it needs to be a part of a chromosome which has a specific sequence known as ‘origin of replication’. Thus, an alien DNA is linked with the origin of replication, so that, this alien piece of DNA can replicate and multiply itself in the host organism. This is known as Cloning or making multiple identical copies of any template DNA.

• The construction of the first recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native Plasmid of Salmonella typhimurium.

• Stanley Cohen and Herbert Boyer in 1972 isolated the antibiotic resistance gene by cutting out a piece of DNA from a plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium. The cutting of DNA at specific locations became possible with the discovery of the so-called ‘molecular scissors’– restriction enzymes.

• The cut piece of DNA was then linked with the plasmid DNA. These plasmid DNA act as vectors to transfer the piece of DNA attached to it.A plasmid can be used as vector to deliver an alien piece of DNA into the host organism.

• The linking of antibiotic resistance gene with the plasmid vector become possible with the enzyme ligase, which acts on cut DNA molecules and joins their ends. This makes a new combination of autonomously replicating DNA created in vitro and known as recombinant DNA.

• When this DNA is transferred into E.coli, it could replicate using the new host DNA polymerase enzyme and make multiple copies. The ability to multiply copies of antibiotic resistance gene in E.coli was called cloning of antibiotic resistance gene in E.coli.

“Recombinant DNA technology” or also called “Genetic Engineering” deals about, the production of new combinations of genetic material (artificially) in the laboratory.  These “recombinant DNA” (rDNA) molecules are then introduced into host cells, where they can be propagated and multiplied.

Steps of  Fecombinant DNA Technology –

I. Identification of DNA with desirable genes.

II. Introduction of the identified DNA into the host.

III. Maintenance of introduced DNA in the host and transfer of the DNA to its progeny.

Tools of Recombinant DNA Technology includes

• Restriction Enzymes

• Polymerase enzymes

• Ligases

• Vectors

• Host organisms

Restriction Enzymes (Molecular Scissors):

Restriction enzymes belong to a larger class of enzymes called Nucleases.  There are of two kinds; Exonucleases and Endonucleases.  Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific position within the DNA.

Example, the first restriction endonuclease – Hind II, always cut DNA molecules at a particular point by recognizing a specific sequence of six base pairs. This specific base sequence is known as the Recognition Sequence for Hind II.

• Each restriction endonuclease recognises a specific palindromic nucleotide sequence in the DNA. Palindromes are group of letters that form the same words when read both forward and backward for example “MALYALAM”.

5′ —— GAATTC —— 3′

3′ —— CTTAAG —— 5′

The palindrome in DNA is a sequence of base pairs that reads same on two stands when orientation of reading is kept the same.

• Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome site between the same two bases on the opposite strands having sticky strand. The stickiness of the strands facilities the action of the enzyme DNA ligase.

• Restriction endonucleases are used in genetic engineering to form recombinant molecules of DNA which are composed of DNA from different sources or genome.

• When cut the same restriction enzyme the resultant DNA fragments have the same kind of Sticky-ends and can be joined together using DNA ligases.

Diagrammatic representation of Recombinant DNA technology

Separation and isolation of DNA fragments

The fragment of DNA obtained by cutting DNA using restriction enzyme is separated by technique called gel electrophoresis. Negatively charged DNA fragments can be separated by forcing them to move towards the anode under an electric field through medium. DNA fragments separate according to their size through sieving effect provided by agarose gel.

• The separated DNA fragment can be visualized after staining the DNA with ethodium bromide followed by exposure to UV light. Separated bands of DNA are separated from agarose gel and extracted from gel, called elution. The DNA fragment purified this way is used for recombination.

Cloning Vector

Plasmids and Bacteriophages is commonly used vector for cloning. They have ability to replicate within bacterial cells independent of the control of chromosomal DNA. Bacteriophages because of their high number per cell, have very high copy numbers of their genome within the bacterial cells.

Following features are required to facilitate cloning into a vector-

a. Origin of replication (ori) – the sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells.This sequence is responsible for controlling the copy number of the linked DNA.

b. Selectable marker-help in the identifying and eliminating non transformants and selectively permitting the growth of the transformants. Transformation is a procedure through which a piece of DNA is introduced in a host bacterium. Generally,the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli.

c. Cloning sites– to link the foreign DNA, the vector need to have single recognition sites for the commonly used restriction enzymes as presence of more than one recognition sites within the vector will generate several fragments, which will complicate the gene cloning. The ligation of foreign DNA is carried out at a restriction site present in one of the two antibiotic resistance genes.

E. coli cloning vector pBR322 showing restriction sites (Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I, Cla I), ori and antibiotic resistance genes (ampR and tetR ). rop codes for the proteins involved in the replication of the plasmid.

Insertional inactivation:
The most efficient method of screening for the presence of recombinant plasmids is based on the principle that the cloned DNA fragment disrupts the coding sequence of a gene.  This is termed as Insertional Inactiviation.

For example, the powerful method of screening for the presence of recombinant plasmids is referred to as Blue-White selection.  This method is based upon the insertional inactivation of the lac Z gene present on the vector.  The lac Z gene encodes the enzyme beta-galactosidase, which can cleave a chromogenic substrate into a blue coloured product.  If this lac Z gene is inactivated by insertion of a target DNA fragment into it, the development of the blue colour will be prevented and it gives white coloured colonies.  By this way, we can differentiate recombinant (white colour) and non-recombinant (blue colour) colonies.

d. Vectors for cloning genes in plants and animals– Agrobacterium tumefactions (pathogen of dicot plant) is able to deliver a piece of DNA known as ‘T-DNA” to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen. Retroviruses in animals have the ability to transform normal cells into cancerous cells. The tumor inducing (Ti) plasmid of Agrobacterium tumefaciens has been modified into cloning vector having no more pathogenic to plant. Similarly retrovirus have been modified into cloning vector for animals.

Competent host (For Transformation with Recombinant DNA)

1)      Simple chemical treatment with divalent calcium ions increases the efficiency of host cells (through cell wall pores) to take up the rDNA plasmids.
2)      rDNA can also be transformed into host cell by incubating both on ice, followed by placing them briefly at 42oC (Heat Shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.
3)      In Microinjection method, rDNA is directly injected into the nucleus of  cells by using a glass micropipette.
4)      Biolistics / Gene gun method, it has been developed to introduce rDNA into mainly plant cells by using a Gene / Particle gun.  In this method, microscopic particles of gold / tungsten are coated with the DNA of interest and bombarded onto cells.
5)      The last method uses “Disarmed Pathogen” Vectors (Agrobacterium tumefaciens), which when allowed to infect the cell, transfer the recombinant DNA into the host.

Processes of Recombinant DNA Technology

Recombinant DNA technology involves several steps in specific sequence-

a. Isolation of DNA

b. Fragmentation of DNA by restriction endonucleases

c. Isolation of a desired DNA fragment

d. Ligation of the DNA fragment into vector

e. Transforming the recombinant DNA into the host

f. Culturing the host cells in a medium at large scale

g. Extraction of the desired product.

•Isolation of Genetic material:Genetic material is isolated from other macromolecules by using enzymes  such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus). DNA that separate out can be removed by spooling. The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease.

• Cutting of DNA at specific location is performed by using restriction enzyme and Agarose gel electrophoresis to check the progression of a restriction enzyme digestion. After cutting sources of DNA as well as vector DNA with a specific restriction enzyme to cut out ‘gene of interest’ from the source DNA.

• Amplification of Gene of Interest using PCR( Polymerase Chain Reaction) to get multiple copies of the DNA or gene of interest in vitro by using set of primers and enzyme DNA polymerase.

Polymerase chain reaction (PCR) : Each cycle has three steps: (A) Denaturation; (B) Primer annealing; and (C) Extension of primers

This repeated amplification is done by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.

• Insertion of Recombinant DNA into the Host Cell/Organism includes making the recipient cells competent to receive, take up DNA present in its surrounding etc. The recombinant DNA bearing gene for resistance to an antibiotic is transferred into E.coli cells, the host cell become transformed into ampicillin-resistance cells.

• Obtaining the foreign gene product – the foreign DNA multiplies in plant or animal cell to produce desirable protein. Expression of foreign genes in host cells involve, optimized condition to obtain recombinant protein. The recombinant cell is multiplied in a continuous culture system in which used medium is drained out from one side while fresh medium is added from the other to maintain the cells in their physiological active phase. A bioreactor provides the optimal conditions for achieving the desired product by providing optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen).

• Downstream Processing involves processes that make the product obtain ready for marketing. This process includes separation and purification called as downstream processing. Suitable preservatives are added to it and send for clinical trial in case of drugs before releasing to market for public use

Class 12 Biology Revision Notes Chapter 10 Microbes in Human Welfare

Microbes are diverse-protozoa, bacteria, fungi and microscopic plants viruses, viroid and also prions that are proteinacious infectious agents. They are found everywhere on earth ranging from soil, air water and some inhabitable places.

Bacteria and fungi can be grown on nutritive media to form colonies, which can be seen by necked eyes and very useful in study of microorganisms.

Microbes cause many diseases in human beings, plants and animals. Several microorganisms are useful to man in diverse ways.

Microbes in household products

a. Microorganisms like Lactobacillus and other commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. The LAB produces acids that coagulate and partially digest the milk proteins. It also improves its nutritional quality by increasing vitamin B12.  In our stomach too, the LAB play very beneficial role in checking disease-causing microbes.

b. The dough is used for making foods such as dosa and idli is fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas. The dough used for making bread is fermented using baker’s yeast (Saccharomyces cervisiae).

c. Cheese, is one of the oldest food items in which microbes were used. The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii. The ‘Roquefort cheese’ is ripened by growing a specific fungus on them for a particular flavour.

Microbes in industrial production

A number of products like beverages and antibiotics involve uses of microbes. Production on large scale requires growing microbes in very large vessels called fermenters.

a. Fermented Beverages- Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce beverages like wine, bear, whisky and rum.. Wine and bear are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth.

b. Antibiotics- they are chemical substances produced by some microbes and can kill or retard the growth of other microbes. Penicillin was first antibiotic to be discovered. Antibiotics have great improved our capacity to treat deadly diseases such as plague, whooping cough, diphtheria and leprosy.

c. Chemical, Organic acids , Enzymes and other Bioactive Molecules are commercially produced by microbes.

Chemicals :

• Aspergillus niger (fungus) – Citric acid
• Acetobacter aceti (bacterium) – Acetic acid
• Clostridium butylicum (bacterium) – Butyric acid
• Lactobacillus (bacterium) – Lactic acid
• Saccharomyces cerevisiae – Ethanol

Enzymes:

• Lipase – used in laundry detergents
• Pectinase and protease – used in bottled juices
• Streptokinase (Streptococcus bacterium) – used as clot buster (to remove clots)

Bioactive molecules:

• Cyclosporin A (Trichoderma polysporum fungi) – used as immunosuppressive agent (for organ transplant patients).
• Statins (Monascus purpureus yeast) – used as blood cholesterol lowering agents.

Microbes in Sewage Treatment

Municipal waste water (sewage) contains large amount of organic matter and microbes which are pathogenic and cannot be discharged into natural water bodies like rivers and streams.

Sewage is treated in sewage treatment plant to make it less polluting by using heterotrophic microbes naturally present in sewage. Sewage treatment is done in two stages-

In primary treatment, floating debris is removed by sequential filtration. Grit (soil and small pebbles) are removed by sedimentation.

Secondary treatment or biological treatment involves passing of primary effluents in large aeration tank to help the growth of aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). These microbes increase the consumption of organic wastes and decrease the BOD (biological oxygen demand)of the effluents.

BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. It measures the amount of organic matter present in the water. Greater the BOD of water more it is polluted.

• Once the BOD of sewage or waste water is reduced, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.

Sludge is passed into large tanks called anaerobic sludge digesters in which anaerobic bacteria digest the bacteria and fungi in the sludge and produce mixture of gas called biogas, which is a mixture of methane, hydrogen sulphide and carbon dioxide.

The effluents from the secondary treatment plant are released into water bodies.

Microbes in Production of Biogas

Biogas is a mixture of gases produced by the microbial activity that can be used as fuel. Certain bacteria that grows anaerobically on cellulosic material produce large amount of methane along with CO2and H2. These bacteria are collectively called methanogens (Methanobacterium).

Biogas Plant – the excreta of cattle (gobar) is rich in methanogens bacteria and is used for generation of biogas also called as gobar gas.

• The technology of biogas production was developed in India mainly due to the efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

Biogas plant consists of a concrete tank in which bio-wastes are collected and slurry of dung is fed.

A floating cover is placed over digester that moves upward when gas is produced. The gas produced is removed and supplied through an outlet pipe for consumption.

The spent slurry is removed through another outlet and used as fertilisers. Biogas plant is more often build in rural areas as large amount of cattle dug is available easily.

Microbes as Biocontrol agent

Biocontrol means use of biochemical method for controlling plant disease and pests. The chemical used as pesticides and insecticides are harmful to human beings and animals.

Biological control of pests and disease is a method of controlling pest on natural prediction rather than chemicals. The organic farmer creates a system where the pests are not eradicated but kept at manageable level by complex system of check and balance within the living and vibrant ecosystem. For example, the Ladybird and Dragonflies are used to get rid of aphids and mosquitoes respectively. On brassicas and fruit tree, to control butterfly caterpillars bacteria Bacillus thuringiensis is used.

Biological control developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma are free-living fungi that are very common in the root systems that control several plant pathogens.

• Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications.

Microbes as Bio fertilisers

Bio fertilisers are organisms that enrich the nutrient quality of the soil. The main sources includes bacteria, fungi and cyanobacteria.

The root nodule formed by Rhizobium bacteria on root of leguminous plants increase the nitrogen level of soil, necessary for various metabolic processes. Azotobacter and Azospirillum are free living bacteria that live in soil and fix atmospheric nitrogen into organic forms.

Symbiotic association of fungi with angiosperm plants (mycorrhiza) also increase the fertility of soil. Glomus form mycorrhiza that absorbs phosphorus from the soil and passes it to the plant. These microbes also provide benefits like resistance to root-borne pathogens, tolerance to salinity and drought.

Cyanobacteria (Nostoc, Anabaena), an autotrophic microbes found in aquatic and terrestrial environment fix atmospheric nitrogen. In paddy field this acts as important bio-fertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

Strategies for Enhancement in Food Production Notes Class 12 Biology Chapter 9

→ The agricultural practice of breeding and raising livestock is termed animal husbandry. It mainly deals with the care and breeding of commercially important livestock like cows, buffaloes, pigs, cattle, horses, sheep, camels, goats, and poultry farming, and fisheries. Bees, silk-worm, prawns, crabs, birds are also used for their products like honey, milk, and meat, etc.

→ The dairy food industry deals with the management of animals for milk production and its products for the consumption of human beings. Milk yield depends on the quality of breeds with high yielding potential and disease-resistant features.

Those processes and systems are practiced which would increase the yield and improve the quality of milk. The cattle should be well housed, given adequate water, and maintained disease-free. Feeding is done with special emphasis on the quality and quantity of fodder in a scientific manner. Cleanliness and hygiene are of paramount importance while milking, storage, and transport of milk and milk products.

→ Poultry includes all those birds which can be raised under domestication for economic purpose. Poultry farming is highly advantageous. It yields quick returns, requires less space, and easy to manage. Birds like chickens, ducks, geese, turkey, etc. are raised for their eggs and meat.

→ Poultry farm management includes the selection of disease-free and suitable breeds, proper and safe farm conditions, proper feeding and water, hygienic and healthy care.

→ To increase the yield and get desirable qualities in animals, breeding of animals is done. A group of animals that are similar in most characters such as general appearance, features, size, configuration, etc. is said to belong to a breed.

→ When breeding is done between the animals of the same breed, it is called inbreeding. When breeding is done between animals of different breeds it is called cross-breeding or out-breeding.

→ Inbreeding is done by carrying out mating between closely related individuals within the same breed for 4 to 6 generations. Superior males and females are identified and mated in pairs. The progeny is evaluated and superior males and females are selected for further mating. This is repeated for some generations, it leads to the development of pure lines. It increases homozygosity. In cattle, a superior female is one that produces more milk and a superior male is one that gives rise to superior progeny.

→ Inbreeding depression occurs because of continued, close inbreeding, which reduces fertility and productivity. This can be solved by outbreeding.

→ The breeding of unrelated animals is called outbreeding. It may be between some breeds with no ancestral link or between different breeds called cross-breeding. It may happen in different species, called interspecific hybridization.

→ Out-crossing is done within the same breed. It helps to overcome inbreeding depression and the best breeding method to increase productivity.

→ Crossbreeding allows the desirable qualities of two different breeds to combine together. The hybrids are either used commercially or allowed to inbreed so as to select a new stable breed that is superior to the existing breeds.

→ Interspecific hybridization allows the mating of male and female, of two different species. The progeny will have the combined features of both the parents, e.g. mule.

→ Controlled breeding is done with artificial insemination. The semen is collected from males and injected into the reproductive tract of females. This helps in desirable mating and ensures good quality progeny. The semen obtained from a single bull can inseminate a few thousand cows at far-off places.

→ Superovulation and embryo transplantation are new techniques employed for cattle improvement. For this, the cow is administered hormones to induce follicle maturation and superovulation. Due to which several eggs are produced per cycle. These are artificially inseminated, the fertilized eggs are surgically removed at an 8 – 32 celled stage and transferred to the surrogate mother.

→ Apiculture is the maintenance of hives of honey bees for honey production. A. dorasata, Apis, florea, A. indica species are reared for honey. It is an age-old cottage industry. Beehives can be kept in courtyards, or bee pastures of some wild shrubs, fruit orchards, and cultivated crops.

It is not labor intensive but it requires some specialized knowledge and training. Before starting apiculture practice, knowledge of the nature and habits of honey bees, selection of suitable location for keeping the beehives, catching and hiving of a group of bees, management of hives during different seasons, handling and collection of honey and beeswax, is very important.

→ Along with honey, honey bees also produce beeswax, which is used for cosmetics, polished, and various other industries. Honey is aromatic, viscid, and sweet material. Its constituents are :
(a) Levulose – 41.80%,
(b) Glucose and fructose (grape sugar) – 35.40%,
(c) Water – 15.43%,
(d) Sucrose – 5.39%,
(e) Bee wax and pollen grains – 1.68%.

Pure honey is dissolved in water, makes a thread through the depth of glass while impure honey gets dissolved in water.

→ Pisciculture is the rearing and breeding of fish. It includes catching, processing, or selling fishes, shellfish, or other aquatic animals such as prawns, crab, oysters, etc. The flesh of fish has 60 – 80% water, 13 – 20% protein, and some amount of fat. Fish is a very good source of protein and forms an excellent food as it has very little fat and more protein, has a good quantity of vitamin A and D, a rich source of iodine, and easily digested than other meals.

→ In addition to providing food, the fishing industry yields a number of by-products that are of commercial importance.
Some are:
(a) liver oil, which is extracted from fish liver. It’s a good source of vitamin A, C, D, and E,

(b) fish meal is prepared from the waste of fish oil or canning industry or whole fish. It is used as a major food for domestic animals. It is rich in proteins, calcium, and phosphorus,

(c) fish proteins are 80-90% proteins with no fats. These are used in icecreams, pharmaceuticals, paints, varnishes, textile, paper, and cosmetics. Fish protein concentrate (FPC) is also used as a diet supplement,

(d) fish flour is used in biscuits, bread, cakes sweets, and soup. It is easily digested by the infants,

(e) fish fertilizers are wastes of fish meal preparation. These are used as manures for tea, coffee, and tobacco plantation,

(f) fish rees are rich in thymine, lecithin, cholesterol, tyrosine, xanthine, hypoxanthine, and vitamin B, C, D, and E. These are valuable foods.

→ Agriculture is the science or the practice of farming or cultivation, reaping, and management of farm products. Horticulture is the branch of agriculture that deals with the art of growing vegetables, fruits, and ornamental plants.

→ Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for

→ cultivation, give better yields, and disease resistant. The main objective of plant breeding is to reproduce new superior crop varieties with respect to crop yield and quality, increased tolerance to environmental stress such as salinity, extreme temperature, and drought, resistance to pathogens like viruses, fungi, and bacteria, and increased tolerance to insect pests.

→ Plants which are both self and cross-pollinated can produce homozygous and heterozygous population and are most suitable of breeding experiments.

→ First of all collection and preservation of all different wild varieties, species, and relatives of cultivated species is done to properly use the natural available genes. The entire collection of plants or seeds with all the diverse alleles for all genes in a given crop is called germplasm collection.

→ The germplasm is evaluated to identify the plants with a desirable combination of characters. Selection is the oldest breeding method and is the basis of crop improvement.

It may be of two types:
(a) Natural selection and
(b) Artificial selection.

Natural selection is a continuous process that is operating in nature. Here the fittest survives and the remaining ones vanish away.

→ In artificial selection, various types of plants are selected from bulk by plant breeders. This is purposefully done to have a better crop from a mixed population, in a. short duration of time as compared to the natural selection process. This may be achieved by mass selection, pure line selection, and clonal selection.

→ Mass selection is based on phenotypes. The best plants from the population are selected at the time of harvesting, with desired traits. The seeds from all such plants are collected and mixed to form a bulk. This process may be repeated for some generations to get the desired improvement.

→ Pure line selection is also called single plant selection. In it, several single plants with desired traits are selected from a population. This is the best method to improve the variety in self-pollinated plants and the crop is of uniform appearance.

→ Clonal selection is used to ensure purity to race, e.g. mangoes, apples, etc., or due to lack of seed formation, e.g. banana. It is the best method for vegetatively propagated plants

→ The plants are selected by using a suitable selection method. These are then multiplied and used further for hybridization.

→ Hybridization is the crossing of two plants differing from each other genotypically in one or more traits.

The purposes of doing hybridization are:
(a) to exploit and utilize the hybrid vigor and
(b) to increase and generate the genetic variations through recombination.

→ In hybridization, greater success is obtained with healthy and vigorous parents. Selfing is done to reduce heterozygosity. The selected inbreeds are used for hybridization.

→ Hybridization involves emasculation and bagging (discussed in Chapter 2) techniques, which are removal of stamens and bagging male and female flowers to prevent foreign pollen contamination. After these crossing is done by collected pollen grains from the male parent and dusting them on stigma. The same desired characters for hybridization are high protein content from one parent and disease resistance from another parent. The hybrid plant is a genetic combination of the two parents.

→ Hybridization is followed by a selection of hybrids that have desired characters. This step needs expertise and careful scientific evaluation. These plants are superior to both the parents. These are further self-pollinated for several generations to attain homozygosity and to ensure that the desired characters will not segregate in the progeny.

→ After successful experimentation, the crop is grown in the research field under ideal fertilizer application, irrigation, and crop management practices. This is followed by testing in farmer’s fields in different locations for three growing seasons. These are evaluated for their yield and quality, disease resistance qualities, etc.

→ Wheat, rice, and maize are the chief cereals of the world. These belong to the Gramineae family. Wheat flour is used for making chapatis, bread, cakes, biscuits, etc. Its straw is used as fodder and for stuffing. Sonalika and Kalyan Sona are two high-yielding and disease-resistant varieties of wheat.

→ Rice is a staple food for half of the world. It is a semi-aquatic crop. It’s used in various preparations like idli, dosa, kheer, etc. It’s straw issued for making hats. Rice flavor is used in the cosmetic industry. IR-8 and Taichung Native-1, Jaya, and Ratna are few varieties of rice.

→ Maize or corn is rich in carbohydrates, fats, and proteins. It lacks binding gluten so can’t be used for bread making. It can be boiled, roasted, or popped up.

→ Smaller grained cereals are called millets, e.g. ragi, Jowar, and Bajra.

→ Sugarcane is a hybrid obtained from crossing between Saccharum Barberi and Saccharum officinarum. It is the chief source of sugar. Baggage (leftover) is used in the fuel and paper industry. The molasses is used in alcohol anti vinegar preparation.

→ Resistance of the host plant is the ability to prevent the pathogen from causing disease. Some plants are disease resistant while some are susceptible, it is determined by the genetic constitution of the host plant. These pathogens Rhay be fungal, bacterial, or viral, e.g. brown rust of wheat (fungi), red rot of sugarcane, late blight of potato (fungi), black rot of crucifers (bacteria), tobacco mosaic, turnip mosaic (virus). Breeding helps to develop disease-resistant varieties and reduce the fungicides and bactericides treatment.

→ Breeding for disease resistance is achieved by the usual steps like screening for disease-resistant plants through germplasm, hybridization of selected parents, selection and evaluation of the hybrids, followed by testing and finally release of new varieties.

→ Due to a limited number of disease resistance genes in a species, conventional breeding has a limited scope. Other breeding methods such as induced mutations, selection among somaclonal variants, and genetic engineering have promising results in producing desirable characters. Initially, mutations are induced in plants, these are screened for disease resistance genes. Such plants are either directly multiplied or used inbreeding.

→ The mutation is a sudden, stable, and heritable change that alters the genotype of an organism. Mutations are induced artificially in plants which change base sequence in genes, creating genetic variation, this results in new traits in the progeny.

→ The application of induced mutations for crop improvement is called mutation breeding. Mutations can be induced chemically or by radiations, e.g. UV rays, X-rays, cosmic rays, gamma rays, ⁶⁰cobalt, and ¹³⁷caesium, nitrous acid, EMS, mustard gas, colchicine, etc.

→ Plant breeding experiments are used for developing pest and insect-resistant varieties. These are dependent on morphologica1, biochemical, and physiological characters of the host plant. For example, hairy leaves are associated with resistance to insect pests, solid stems of wheat are resistant to stem sawfly, sugar content in maize leads to resistance for maize stem borers. Breeding methods are the same as discussed earlier.

→ Plant breeding is also practiced for improved food quality, it is done for improving protein content and quality, oil content, and quality, for increasing vitamin content, for micronutrient and mineral content. For example, Atlas 66 wheat has high protein content, maize hybrids with more amino acids, lysine and tryptophan and rice with more iron content have been developed.

→ Single-cell proteins (SCPs) are an alternative source of proteins for animal and human nutrition.

→ Microbes like spirulina which can be grown on waste materials can serve as rice food for proteins, minerals, fats, carbohydrates, and vitamins and reduces environmental pollution too. Microbes are grown increasingly on large scale to serve as a good source of proteins.

→ Plant tissue culture is a technique of growing cells, tissues, or organs in sterilized nutrient media under controlled aseptic conditions. The plant part which is used for culture preparation is called explant. Plant cells are totipotent i.e: they can form a complete plant under suitable conditions. In specific culture medium and sterile conditions, many plant cells and tissues divide and grow to form an unorganized mass of cells called callus.

→ The nutrient medium must provide a source for carbon and inorganic salts, vitamins, amino acids, and growth regulators like cytokinins and auxins, etc.

→ Micropropagation or cloning is a novel technique devised to produce vast quantities of strong and healthy plantlets by rapid vegetative multiplication under controlled conditions. Each of these plants is genetically identical to the parent plant and is called some clones.

→ Tissue culture is useful for

1. Micropropagation,
2. Production of disease-free plants,
3. Androgenic haploids and their use in breeding,
4. Embryo rescue for successful hybridization,
5. Induction and selection of mutants,
6. Somaclonal variations,
7. Protoplast technology.

→ Culture of explant on an agar medium containing 2, 4-D results in the formation of callus. Suspension cultures are obtained by culturing pieces of callus in a liquid medium which is constantly agitated so that the larger masses are dissociated into smaller clumps and single cells.

→ The callus and suspension cultures are commonly used for achieving cell biomass production. Single cells can be isolated either from suspension culture or directly from explants by mechanical or enzymatic methods. They are cultured in liquid or semi-solid media by using filter paper raft-nurse tissue technique or by Bergmann’s plating technique. Plantlets can be regenerated from callus or suspension cultures either by shoot regeneration or by somatic embryo regeneration technique.

→ The regenerated plantlets can be transferred and established in the field. The term ‘micropropagation’ or ‘cloning’ is applied to a novel technique devised to produce vast quantities of strong and healthy plantlets by rapid vegetative multiplication under controlled conditions.

Haploid plants can be produced by another culture or by culturing microspores. These haploids can be converted to homozygous diploids by doubling their chromosomes using certain chemicals.

→ Young embryos can be cultured on artificial culture media containing specific nutrients. This technique is helpful in raising the plants from interspecific crosses as well as for ‘embryo rescue’. The multiple shootlet production techniques are useful in getting disease-free healthy plants.

→ Genetic vacations occur at all levels of the tissue culture process. They are termed somaclonal variations. These variations are useful for the improvement of crops if they are heritable and have agronomic traits.

→ Naked protoplasts of plant cells can be isolated by digesting their cell walls using certain hydrolytic enzymes. The isolated protoplasts can be cultured in a liquid or semi-solid medium. Naked protoplasts of two different plants can be allowed to fuse to form hybrids. This is called protoplast fusion and somatic hybridization.

The plant tissue culture technique is also used for the production of artificial seeds in those plants which either do not bear seeds or produce a small number of seeds.

→ Artificial seeds are used for direct field delivery of select elite genotypes, hand-pollinated hybrids, genetically engineered plants, sterile and fertile genotypes, etc.

→ Cultivation of plant cells in culture media promises great potential in large-scale production of secondary metabolites which are otherwise produced in minute amounts and their extraction from the plants is difficult and expensive.

→ Allotetraploid: AllotetraploidS are produced by the multiplication of chromosomç sets that are initially derived from two different species.

→ Apiculture: Rearing and management of beehives for obtaining honey and wax.

→ Aquaculture: Production of useful plants and animals.

→ Concentrates: They include cotton seeds, oil cakes, cereal grains, etc.

→ ElectrapOration: Genetic transformation by applying high electric potential for a few microseconds to change the porosity of protoplast to take up DNA.

→ EmasculatiOn: Removal of stamens from bisexual flowers before they burst and shed their pollen.

→ Hybrid vigor: The increased vigor often exhibited by hybrid progeny.

→ Livestock: The animals like cattle, sheep goat, camel, horse, pig, and poultry form livestock.

→ Pisciculture: The rearing of fishes for obtaining meat and oil.

→ Poultry: Rearing of fowls, ducks, turkeys for their eggs and meat.

→ Roughage: It includes straw of cereals such as wheat, rice, Jowar, and oat, etc.

Human Health and Disease Notes Class 12 Biology Chapter 8

→ Health is a state of complete physical, mental and social well-being. It is not just the absence of diseases. Health may be defined as a state of the body when all the organs and systems are functioning properly and a perfect balance is maintained between the environment and the body.

→ The disease may be identified as any condition which impairs health or interferes with the normal functioning of the body due to one or another reason. It is any functional change from the normal state which causes discomfort or disability.

→ Any factor or substance which causes disease by its excess or deficiency or absence is called a disease agent.

→ The disease agents may be biological (e.g. virus, bacteria, fungi, protozoans, helminths, and anthropods) they are called pathogens; or Nutrient agents, e.g. food components viz. proteins, fats, carbohydrates, minerals, vitamins, and water; or chemical agents, may be exogenous or endogenous ones. Exogenous agents enter the body from outside e.g.-pollutants such as fumes, dust, metals, gases, etc., or allergens such as pollen and spores.

Endogenous chemical agents are formed inside the body, e.g. hormones, enzymes, uric acid, etc.; or Physical agents such as humidity, pressure, radiation, heat, cold, electricity, and sound; or mechanical agents such as chronic friction or other mechanical forces which cause a sprain, fracture or dislocation, etc; err genetic agents which cause genetic disorders or underdeveloped organs.

→ Diseases are broadly classified into two types as

1. Congenital disease and
2. Acquired diseases.

→ Congenital disease is anatomical or physiological abnormalities that are present at the time of birth. These may be single gene mutation, e.g. phenylketonuria, albinism, sickle-cell anemia, color blindness, hemophilia, etc., or chromosomal aberrations e.g. Down’s syndrome, Klinefelter’s syndrome, or Turner’s syndrome. These are further transmitted to the children.

→ Harelip and cleft palate are some environment-related congenital diseases that are not transferred to children.

→ Acquired diseases: These develop after birth. They may be communicable or non-communicable diseases.
Classification:

→ Acquired diseases are further of two types – Communicable and non-communicable. Communicable diseases are infectious which are caused by pathogens. Non-communicable diseases are non-infectious ones that remain confined to the diseased person only.
These are of four types:

1. Organic diseases occur due to the malfunctioning of important organs such as heart diseases, epilepsy.
2. Deficiency diseases are produced by a deficiency of minerals, nutrients, vitamins, and hormones such as beriberi, diabetes, goiter, etc.
3. Allergies are caused when the body becomes hypersensitive to some foreign substance e.g. Hay fever,
4. Cancer is caused by the uncontrolled growth of certain tissues in the body.

→ Communicable diseases are classified into seven types:

1. Viral diseases e.g. smallpox, chickenpox, polio, common cold, etc.
2. Rickettsial diseases are caused by obligate intracellular parasitic organisms known as rickettsias, e.g. typhus fever, Q fever, Rocky Mountain spotted fever, etc.
3. Bacterial diseases e.g. diphtheria, tetanus, food poisoning, etc.
4. Spirochaetal diseases are caused by long, spiral, corkscrew-shaped bacteria called spirochaetes e.g. syphilis,
5. Protozoan diseases are caused by protists, e.g. amoebic dysentery, malaria, kala-azar, sleeping sickness, etc.
6. Fungal diseases are caused by non-green heterotrophic organisms, fungi e.g. ringworm and athlete’s foot,
7. Helminth diseases are caused by flatworms and ringworms e.g. liver rot, taeniasis, etc.

→ Typhoid is caused by gram-negative bacteria, Salmonella those commonly found in the human intestine. It is a communicable disease, spread through the intestinal discharge of typhoid carriers. Its incubation period is 1 – 3 weeks.

Its symptoms include headache, typical typhoid fever which increases in the afternoon and enhances every day, in a second week its high and decreases during the third and fourth week, lesions of the intestinal mucosa, hemorrhage, ulcer of the intestine, red rashes on chest and upper abdomen. It is confirmed by S.typhi bacterium detection in stools or blood and also by the Widal test.

As typhoid spreads through contaminated food and water, precautions should be taken for screening of water and food sources, proper sanitation of human feces.
Its therapy includes

1. Thyphoral is an oral vaccine,
2. TAB – this vaccine provides immunity for 3 years,
3. Chloramphenicol, ampicillin, and chloromycetin are effective drugs against typhoid bacterium.

→ Pneumonia is a lung infection caused by bacteria like Streptococcus pneumonia and Haemophilus influenza or mycoplasma or viruses. This is an airborne disease spread through cysts present in the patient’s sputum. Its incubation period is 1 – 3 days. Pneumonia is characterized by lymph collection and mucus in the bronchioles and alveoli, thus decreasing the respiratory efficiency of the lungs. It includes fever, chills, cough, and headache. In severe cases, the fingernails and lips may turn grey to bluish.

The bacteria present in the body secretion of the patient are released out as aerosols or droplets which are inhaled by healthy person and cause infection. It also spread by glasses and utensils sharing with the patient so the best precaution is the isolation of the infected person. It is treated, with penicillin, flucloxacillin, etc. antibiotics.

→ The common cold is caused by a large number of viruses that belong to a group ‘rhinoviruses. It is the most infectious human disease. These viruses infect the nose and respiratory passage but not the lungs of the patient. Its symptoms are nasal congestion, discharge, sore throat, cough, headache, tiredness, etc. It lasts for 3 to 7 days. The infection spreads through droplets from sneezes or cough, through contaminated objects like books, cups, doorknobs, computer keyboard pens, mice, etc.

Salmonella typhosa

Diplococcus pneumoniae

→ Amoebic dysentery or Enteritis or Amoebiasis is caused, by an intestinal endoparasitic protozoan, Entamoeba histolytic which inhabits the large intestine. It may also spread to the lower part of the small intestine, liver, lungs, and brain. E. histolytic occurs in two forms (diagonal) minute form, its an absorptive stage and undergoes encystment and magma form, its large-sized, destroys epithelial cells and holozoic stage. Its main sources of infection are drinking water and food, contaminated by the fecal matter of infected person. Houseflies act as carriers and transfer the parasite from feces to food products.

Stool detection of the patient shows the presence of E. histolytic. The symptoms include constipation, abdominal pain, and cramps, stools with excess mucous, and blot clots. The protozoan secretes leading to ulcers.

Its precautions include

1. proper sanitary conditions,
2. coverage of tables to prevent contamination by vectors,
3. proper washing of fruits and vegetables before eating. Its treatment is done by antibiotics like Terramycin, erythromycin, aureomycin, and metronidazole.

→ Malaria is a vector-borne disease which is caused by the protozoan parasite Plasmodium. It is caused by toxic pigment hemozoin from RBC’s Hb. This is produced when RBC are destroyed by developing stages of the Plasmodium. Plasmodium is digenetic (two hosts) and triphasic. The primary host is the female Anopheles mosquito and the secondary host is human beings.

Three phases include asexual schizogony (in liver and RBCs of man), sexual cosmogony (starts in RBCs and completes in mosquito’s stomach), asexual sporogony (stomach of mosquito). Malaria is of several types which are caused by different species of Plasmodium. Malaria caused by Plasmodium falciparum is most dangerous, it is called malignant malaria and it can be fatal.

Plasmodium enters the human body through the Anopheles mosquito. The parasite multiplies within the RBCs and ruptures the cells. Symptoms include headache, chill, shivering, nausea, muscular pain, recurring fever every 3rd or 4th day, increase in pulse and respiration rate, sweating, and anemia.

Its symptoms are divided into three stages:

1. cold state,
2. hot stage and
3. sweating stage.

The mosquitoes acquire the parasite from infected persons and transmit it to healthy individuals.

Its precautions include

1. wire gauzing of doors and windows etc.,
2. using mosquito nets,
3. use of mosquito- repellents.
4. spraying insecticides like D.D.T. and B.H.C.,
5. do not allow any stagnant water. Its treatment is done by quinine, chloroquine, palustrine, Daraprim, etc., anti-malarial drugs.

→ Filariasis is caused by the filarial worm, Wuchereria ban crafti and Wuchereria malayi. The worm is digenetic, its primary host is man, and the secondary or vector host is mosquitoes Aedes and Culex. It causes slowly chronic inflammation of organs for many years.

They are found in lymph vessels and lymph nodes and due to infection the lymphatic vessels of lower limbs become enlarged due to blockage and chronic inflammation. The disease is called elephantiasis or filariasis. Genital organs are also affected. This causes enormous swelling of legs, scrotal sacs, breasts, etc.

The pathogens are transmitted through the bite of female mosquito vectors. Its precautions are the same as for malaria. Its treatment includes Hetrazan and diethylcarbamazine.

→ Ascariasis is caused by intestinal endoparasite of man, Ascaris lumbricoid known as roundworm. It is a monogenetic helminth that spreads through water, vegetables, fruits that are contaminated with the eggs of the parasite. Its symptoms include abdominal pain, indigestion, weakness, anemia, nausea, vomiting, diarrhea, internal bleeding, muscular pain, fever, etc.

Heavy infection may cause pneumonia, hepatitis, blockage of the intestine, convulsions, etc. Flies and cockroaches serve as vectors for spreading the diseases. It is diagnosed by doing stool test, Dermol test or Scratch test, its precautions are same as for Amoebic dysentery. Its treatment is done by Hexyl-resorcinol crystals, a mixture of oil of chenopodium and tetrachloroethylene.

→ Ringworms are a common infectious disease caused by fungi Microsporum, Trichophyton, Candida, and Epidermophyton. Their symptoms include dry and scaly lesions on skin, nails, and scalp. These are accompanied by intense itching.

Moisture and warmth help in fungal growth. It’s most likely to grow in skin folds like the groin and between the toes. These generally spread from soil or sharing towels, clothes, or comb with an infected person. These are treated with antifungal ointments.

→ Vaccination is a common method of preventing the infection of microorganisms like bacteria and viruses. Infectious diseases like polio, diphtheria, pneumonia, and tetanus are controlled to great extent by vaccination. Smallpox is completely eradicated by vaccines and immunization programs. Various antibiotics are also very effective against infectious diseases.

→ Disease resistance or immunity is the ability of an organism to resist disease. Immunology is the branch of science which deals with immunity. The immune system forms the third line of defense. The immune system can differentiate between self (body cells) and non-self (foreign microbes).

→ Any foreign substance entering the body stimulates an immune response it is called an antigen. The protective chemicals (proteins) produced by the body in response to antigens are called antibodies.

→ Immunity is of two main types:

1. Innate immunity and
2. Acquired immunity.

1. Innate immunity or inborn or natural immunity is non-specific and present at the time of birth. It is inherited from the mother through the placenta. It provides four different types of barriers to the foreign agents as (a) physical barriers: Skin is the foremost barrier that prevents the entry of microorganisms, similarly, the mucus coating of the epithelial layer lining the respiratory, gastrointestinal, and urogenital tracts also defend the entry of microorganisms,

2. Physiological barriers such as gastric acids, saliva in the mouth, tears, all prevent microbial growth.

3. Cellular barriers, some leukocytes (WBC) like polymorphonuclear leukocytes (PMNL-neutrophils) and monocytes and some lymphocytes (e.g. natural killer) from blood and macrophages from tissue can phagocytose and destroy the invading microbes,

4. Cytokine barriers, virus-infected cells produce anti-viral proteinous molecules called interferons, which protect the unattacked cells from viral attack.

→ Acquired or adaptive immunity is not present from birth but is acquired or developed by the organisms in response to a disease. It is pathogen-specific and is characterized by memory. When the body encounters any antigen (pathogen) the lymphocytes produce antibodies which are termed as a primary response, it’s of less intensity.

Lymphocytes also provide immunity against further attack, a subsequent encounter with the same pathogen produces a highly intensified secondary or anamnestic response. The acquired immunity may be temporary (influenza) or permanent (measles, mumps, polio, smallpox, etc.) for life long.

→ Acquired immunity is of two types:

1. Active or natural immunity is developed by antibodies from the individual’s body,
2. Passive or artificial immunity: In it, readymade antibodies are obtained from human or animal serum, who had recovered from the same infection and injected into the patient. It is known as inoculation
   e.g. tetanus treatment, snake bite, etc.

→ The primary and secondary immune responses are carried out with lymphocytes. Lymphocytes are a kind of agranulocytes of leucocytes (WBC) of blood. Lymphocytes are of two types: B-lymphocytes and T-lymphocytes. Both types of lymphocytes are formed from the stem cells called haemocytoblasts in the bone marrow and undergo further processing.

Showing formation of lymphocytes

→ B-lymphocytes produce antibodies when stimulated by an antigen. After stimulation one B-lymphocyte synthesize RNA, divide rapidly and differentiate into the RER-rich histologically distinctive plasma cells. A group of plasma cells is called a clone. They produce antibodies at a rate of about 2000 molecules per second. These antibodies circulate in the lymph to fight antigens. They form the humoral immune system or Antibody-Mediated Immune System (AMIS).

→ An antibody molecule is made up of four peptide chains, two small peptide chains called light chains, and two long heavy chains. An antibody may be designated as H₂L. There are five classes of antibodies (immunoglobulins) namely IgM, IgG, IgA, IgD, and IgE. IgG is not abundant in man whereas IgM and IgG cause the lysis of foreign cells.

→ The second type of acquired immune response is Cell-Mediated Immune System (CMIS). It is mediated by T-lymphocytes. T-cells do not secrete antibodies but help B-cells to produce them. T-lymphocytes attack directly the pathogenic microorganisms entering the body or grafts such as transplanted kidney or skin grafts. It also protects the body from its own cells which have become cancerous.

→ Vaccination or immunization is based on the property of memory of the immune system. A preparation of antigenic proteins of pathogen or weakened or inactive pathogen is given. The body produces antibodies against these antigens and neutralizes the pathogenic agent during actual infection. The vaccines also produce memory B and T cells which recognize the pathogen or subsequent exposure and counteract with massive production of antibodies. Vaccines are also produced by recombinant DN A technology where bacteria or yeast produce antigenic polypeptides of pathogens, e.g. hepatitis B vaccine.

→ Allergies are an exaggerated immune response to certain antigens called allergens e.g. dust mites, pollens, animal dung, fur, venom, etc. Allergy symptoms are inflammation of mucous membranes, sneezing, watery eyes, running nose, irritation of upper respiratory tract, rashes, itching, etc. In allergic people, the body develops a primary immune response on encounter with the allergen. B-cells produce antibody IgE. On the next exposure, the body produces a secondary immune response called allergy.

→ The allergens combine with antibody-bound mast cells and basophils. This complexing ruptures the mast cells and basophils, releasing histamine from vesicles called granules. The process of the release of histamine is termed degranulation. The histamine acts as an allergy mediator. It increases the permeability of capillaries constricts smooth muscles in many parts such as those around the bronchioles, causing breathing problems; and stimulates mucous glands. It also widens the small arteries but not the veins.

Thus, the affected area (where histamine has been released receives more blood than it returns. As a result of this, fluid accumulates in the tissue which swells up. This causes allergy.

Showing allergic reaction and release of histamines by rupturing of mast cells

→ The immune system sometimes rejects certain tissues of the body as non-self. Due to genetic and other unknown reasons the body attacks self-cells. This is called autoimmunity. The body tissues act as autoantigens and autoantibodies, e.g. Hashimoto’s thyroiditis, systemic lupus erythematosus, rheumatoid arthritis.

→ The immune system plays a role in allergic reactions, autoimmune diseases, and organ transplantation. The immune system consists of lymphoid organs, tissues, cells, and soluble molecules like antibodies. Lymphoid organs help in the origin or maturation and proliferation of lymphocytes.

The primary lymphoid organs are bone marrow and thymus, here immature lymphocytes differentiate into antigen-specific lymphocytes. After maturation lymphocytes migrate to secondary lymphoid organs which are the spleen, lymph nodes, tonsils, appendix, and Peyer’s patches of the small intestine. Here the lymphocytes interact with antigens and then proliferate to become effector cells.

→ Bone marrow provides a suitable environment for the development and maturation of B-lymphocytes. Bone marrow is the main lymphatic organ where all blood cells, as well as lymphocytes, are produced.

→ The thymus is a lymphatic organ, located near the heart beneath the chest bone. It is prominent in children but keeps on reducing with age, by puberty it becomes very small in size. Development and maturation of T-lymphocytes take place in the thymus. It educates the fetal lymphocytes to distinguish between self and non-self.

→ The spleen is the largest component of the lymphatic system. It is bean-shaped, vascular, dark red in color, located in the abdomen below the diaphragm. It consists of red pulp and white pulp. It helps in the destruction of worn-out RBCs, as a reservoir of RBCs, production of antibodies, disposal of foreign elements.

→ Lymph nodes are present at intervals in the course of lymphatic vessels. They contain lymphocytes, plasma cells, and macrophages. They trap the microorganisms and antigens and stimulating the immune response.

→ Lymphatic tissue present in the lining of respiratory, digestive, and urogenital tracts is known as mucosal-associated lymphoid tissue (MALT). Lymphatic tissue present in the gut is called get-associated lymphoid tissue (GALT).

AIDS is an acquired immunodeficiency disease. A detailed account of the retrovirus and the disease has been discussed in detail in previous chapters. Its control and prevention were also discussed.

The figure shows the aids virus.

Diagram of AIDS virus

Cancer is a malignant growth or tissue enlargement due to unlimited and uncontrolled mitotic division of some cells known as cancerous cells.

Showing development stages of cancer due to smoking in lung epithelium

Cancerous cells grow rapidly and form a mass of cells called tumors. Tumors are of two types: Benign or non-malignant tumors these remain confined to one place and cause little damage, cancerous or malignant tumors – these are a mass of proliferating cells known as neoplastic cells. They grew rapidly, damage the nearby normal tissue. Cancerous cells divide actively and compete for nutrients with the normal tissue. These cells reach another place through blood and form new tumors. This is called metastasis.

→ Cancer is neither contagious nor hereditary. Factors that cause cancer are called carcinogenic agents. These may be ionizing radiations, e.g. x-rays and gamma rays or non-ionizing rays like U.V rays, chemical carcinogens like beetle and tobacco, aniline dyes, heavy smoking, viral oncogenes, and cellular oncogenes. Cellular oncogenes (c-onc) or protooncogenes are present in normal cells which get activated under certain conditions and become oncogenes.

→ Detection of cancer is done by biopsy and histopathological studies of tissues, blood, and bone marrow for increased cell count (leukemia). X-rays, CT scans, and MRIs are used to detect cancer of internal organs. Mammography is done to detect breast cancer. Pap test is done for cancer detection in the cervix and other genital parts. Monoclonal antibodies against the cancer-specific antigen are coupled to the suitable radioisotope, these antibodies are used further for cancer detection.

→ Cancer is treated with surgery, radiation therapy and immunotherapy, and chemotherapy. Biological response modifiers such as γ – interferons are used to activate the immune response to destroy the tumor.

→ Drugs are normally used for the treatment of diseases. An addictive drug modifies the biological, psychological, or social behavior of an individual by stimulating, depressing, or distorting mind and body functions. This habit of taking drugs beyond voluntary control is called an Addition. Commonly abused drugs include opioids, cannabinoids, and coca alkaloids.

TABLE: SHOWING MAJOR GROUPS OF PSYCHOTROPIC DRUGS WITH EXAMPLES AND EFFECTS

Type of Drug	Examples	Effects
I. Sedatives and tranquillisers (depressant)	Benzodiazephines {eg.. Valium) Barbiturates	Depress brain activity and produce feelings of calmness relaxation, drowsiness, and deep sleep (high doses).
II. Opiate narcotics	Opium Morphine. Heroin Pethidine. Methadone	Suppresses brain function, relieves intense pain.
III. Stimulants Caffeine (very mild).	Cocaine. Amphetamines	Stimulates the nervous systems makes a person more wakeful, increases alertness and activity, produces excitement.
IV. Hallucinogens	LSD. Mescal in. psilocybin. Bhang. Ganja. Charas. Marijuana	Alters thought feelings and perceptions cause illusions.

Opioids bind to opioid receptors in the central nervous system and gastrointestinal tract. These suppress brain activity and relieve pain. These are called pain killers e.g. opium and its derivatives.

(a) Somniferum (Opium poppy) plant (b) Chemical structure of Morphine

Heroin or smack is diacetylmorphine. It is a white, odorless, bitter crystalline compound. It is formed by the acetylation of morphine, which is extracted from poppy latex. It is a depressant and slows down body functions.

→ The products of the Hemp plant Cannabis Sativa are Bhang, Ganja, Charas, Hashish, and Marijuana. These are less harmful but may lead to opiates addiction. Their active compound is delta-9- tetrahydrocannabinol or THC.

(a) Leaf of Cannabis Sativa
(b) Skeletal structure of cannabinoid molecule

Cocaine or coke is an alkaloid from Erythroxylum coca. It has a potent stimulating effect on the central nervous system, produces a sense of euphoria and increased energy.

→ Datura spp. and Atropabeliadona also have hallucinogenic properties. Cannabinoids are misused by some sportspersons.

→ Other abused drugs are barbiturates, amphetamines, benzodiazepines, and lysergic acid diethyl amides (LSD).

→ The adolescence period is very vulnerable to the mental and psychological development of an individual. Curiosity, adventure and excitement, and experimentation motivate youngsters towards drug and alcohol misuse.

TABLE: SHOWING EFFECTS OF ALCOHOL AND DRUGS

Combination	Effect
Alcohol + barbiturates	Dramatically increased depressant effect
Alcohol + antihistamines	Marked drowsiness
Alcohol + Valium	The rapid increase in the sedative effect
Alcohol + Marijuana or Hashish	Decreased coordination, increased reaction time, impaired judgment
Alcohol + Aspirin	Increased risk of damage to the gastric mucosa

→ Smoking paves the way to hard drugs. Tobacco is derived from Nicotiana tabacum and N, Rustica leaves. Its main constituent is the toxin alkaloid Nicotine. It stimulates the release of adrenaline and nor-adrenaline which cause high blood pressure and increased heartbeat. It is associated with lung cancer, bronchitis, emphysema, coronary heart disease, urinary bladder cancer, throat cancer, gastric ulcer, and oral cavity cancer.

→ Alcohol is obtained from the fermentation of cereals or grains by yeast Saccharomyces cerevisiae and further distillation. It has depressant effects on the central nervous system.

→ The symptoms of addiction include undue excitement, irritable and violent nature, exhausted and drowsy appearance, loss of interest in studies, poor concentration and memory, reduced appetite, vigor, and weight.

→ Parents should keep a watch on their children and seek medical and professional help if needed.

→ Allografting: A graft taken from another person. e.g. skin.

→ Antibody: The proteinous molecules produced to counter the specific antigen.

→ Antigen: A foreign agent which stimulates the immune system to produce antibodies.

→ ARC: AIDS-related complex.

→ Autoimmunity: An immune disorder when the immune system of a person rejects its own body cells.

→ Addiction: Dependency on certain drugs.

→ Anesthetic: Chemical which causes the loss of sensation, e.g. opiates.

→ Benign tumor: Cäncer type which remains localized in the organ affected.

→ Communicable disease: The disease which can be transmitted from an infected person to a healthy person.

→ Cancer: Disease characterized by uncontrolled growth and division leading to tumor formation.

→ Carcinogens: Cancer-causing agents e.g. radiations.

→ Carcinomas: Cancers located in the epithelial tissues. e.g. breast cancer.

→ Congenital diseases: Inborn diseases caused by gene or chromosomal mutations, e.g. hemophilia.

→ Cirrhosis: A liver disease caused by the storage of fats.

→ Co-poisoning: CO of tobacco smoke binds lib of RBCs and decreases their Oxygen carrying capacity.

→ Depressant: Chemical which lowers the activity of CNS, e.g. alcohol.

→ Disease: A condition impairing health.

→ Epidemiology: Mode of transmission of disease.

→ Epidemic: A disease that attacks a large number of people at the same time and in the same region e.g. cholera.

→ Endemic: A disease restricted to a certain region, e.g. sleeping sickness.

→ Gastritis: Inflammation of gastric mucosa.

→ hallucinogens: Chemicals which change thoughts, feelings, and perceptions of a person e.g. LSD.

→ Health: A state of complete physical, mental and social norms.

→ Hypertension: High blood pressure.

→ Immunodeficiency: An immune disorder characterized by a deficiency of B-cells and T-cells in the body.

→ Immunoglobulin: Antibodies (γ-globulins) produced against the antigen.

→ Immunity: Resistance of body towards diseases.

→ Immunosuppression: Immune disorder in which the immune system rejects transplanted organs.

→ Infection: Entry and multiplication of living pathogenic microorganisms in some part of the host’s body.

→ Infestation: Presence of a large number of parasitic organisms on the surface of the host’s body or clothing.

→ Incubation period: Period between infection and appearance of the first symptom of a disease.

→ Leukemia: Blood cancer, increased WBC count of the blood.

→ Metastasis: Spread of cancer.

→ Lymphocytes: Type of WBCs which produce antibodies.

→ Lysozyme: A bacterial protein.

→ Neoplasm: A tumor formed by uncontrolled growth of the tissue in cancer.

→ Neuritis: Inflammation of nervous tissue of the brain.

→ Oncogenes: Cancer-causing genes.

→ Prophylaxis: Prevention of occurrence of a disease.

→ Psychotropic drug: mood-altering drug.

→ Pyrexia: Increase in temperature.

→ Pathogen: An organism causing disease.

→ Pyrogen: A fever-causing substance.

→ Serology: Study f antigen-antibody interactions.

→ Sedative: A chemical that decreases functional efficiency and has a calming effect, e.g. alcohol.

→ Therapy: Mode of treatment of a disease.

→ Tranquilizer: A drug having a calming effect without inducing sleep e.g. valium.

→ Vaccine: An inoculation with dead or weakened or virulent germs, which stimulates the formation of antibodies of the host’s body.

→ Vector: Organism which spreads the disease.

Class 12 Biology Revision Notes Chapter 7 Evolution

Evolutionary biology is the study of history of life forms on earth. The evolution of life on earth, different changes in flora and fauna around earth that co-exist along with human beings also forms parts of evolution.

Origin of Life

The origin of life is considered unique events in the history of universe. Huge cluster of galaxies comprises the universe. Galaxies contain stars and clouds of dust and smoke.

Big Bang Theory attempts to explain the origin of universe. According to this theory, a huge explosion occurs that forms the different galaxies.

In solar system of Milky Way galaxies, earth has been supposed to be formed about 4.5 billion years ago. There was no atmosphere in early earth. Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the earth surface.

UV rays from sun splits the water into hydrogen and oxygen. Life appeared 500 million years after the formation of earth.

There are different theories regarding the origin of life on earth-

• Some scientist believes that life comes from other planets. Early Greek thinker thoughts that unit of life is called spores transferred from other planets.
• According to other theory, life comes out of dead and decaying matters like straw and mud. This theory is called theory of spontaneous origin.
• Louis Pasture experimentally proved that life arises only from pre-existing life. Spontaneous theory of origin of life is dismissed after that.
• Oparin and Haldane proposed that the first form of life could have come from pre-existing non-living organic molecules like RNA and protein etc. The formation of life preceded by chemical evolution. At that time condition on earth were- high temperature, volcanic eruption, reducing atmosphere containing CH4and NH3.

Miller experiment of Origin of Life- S.L. Miller in 1953, conducted an experiment to show the origin of life on earth in the physical environment similar to condition prevails at that time.

Miller created similar condition of temperature and pressure in laboratory scale. He created electric discharge in a flask containing CH4, H2 and NH3 and water vapour at 8000C.

He observed formation of amino acids in flask after 15 days of electric discharge. Similar experiment by other scientist found formation of sugars, nitrogen bases, pigments and fats.

Analysis of meteorite content also reveals similar compounds that reveal that similar process are occurring elsewhere in the space. This experimental evidence about the origin of life is called chemical evolution of life.

Experimental representation of Miller’s experiment

The first non-cellular forms of life could have originated 3 billion years back. They could have been giant molecules like RNA, Protein, and Polysaccharide etc.

The cellular form of life was probably single cell and originates in water medium. The theory that first form of life arose slowly through evolutionary forces from non-living molecules is called biogenesis.

Evidence of Evolution: Evidence that evolution of life forms has taken place on earth have many proofs as mentioned below-

1. Paleontological evidence- different aged rock sediments contain fossils of different life forms that probably died during the formation of particular sediment. Fossils are remains of hard parts of life-forms found in rocks .The study showed that different form varied over time and certain life forms are restricted geological time span. Hence, new forms of life have arisen at different times in history of earth.

2. Homologous organs- those organs that perform different function but have similar origin and structure are called homologous organs. For example human, cheetah, bat and whales share similarities in pattern of bones of forelimbs although these forelimbs perform different functions in these animals. In these animal similar structure developed along different directions due to adaptation of different needs. This is called divergent evolution.

Homologous structures	Analogous structures
Similar in anatomy	Dissimilar in anatomy
Doing dissimilar functions	Doing similar functions
Develop in related animals	Develop in unrelated animals
Inherited from a common ancestor	Not inherited from common ancestor
Similar developmental pattern	Developmental pattern is not similar
Similar structure and Origin	Dissimilar in structure and origin

3. Analogous structures-they are not anatomically similar organs but perform similar function. For example eyes of mammals and octopus or flippers of penguin and dolphins. This is due to similar habitat that resulted in similar adaptive features in different groups of organisms. This that of evolution is called convergent evolution.

4. Biochemical evidences – similarities in proteins and genes performing a given function among diverse organisms give hints to common ancestry. These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms.

DIVERGENT EVOLUTION	CONVERGENT EVOLUTION
1. Development of different functional structures from a common ancestral form is called divergent evolution.	Development of similar adaptive functional structures in unrelated groups of organisms is called convergent evolution.
2. Homologous organs show divergent evolution.	Analogous organs show convergent evolution.
Examples.: Darwin’s Finches, Australian Marsupials, locomotion in mammals.	examples. Australian Marsupials and Placental mammals, various equatic vertebrate and wings of insect bird and bat.

Evolution by natural selection- Industrial melanism
A case of natural selection was seen in England in 1850s, i.e., before industrialisation in a peppered moth (Biston betularia). This moth had two forms: grey colour and black colour (Carbonaria). In the early part of the nineteenth century , before industrialization only the grey coloured forms of moths were present; the dark forms were rare. The grey coloured moths were seen on the tree trunks covered with lichens and so they were able to escape from their enemies. Later on in 1920, due to the development of industries, post industralization, the lichens were killed and the tree trunks looked dark due to the deposition of industrial soot. Birds, now were able to spot these moths and feed upon them. So the grey coloured moths were eaten by the birds and the dark coloured moths escaped from the birds. Then now the coal is replaced by the industries and oil and electricity is used. This has reduced the soot production and ultimately less deposition of soot on the tree trunks. These tree trunks have, now, again become grey in colour. Consequently, grey coloured moths have again increased in number. This example clearly brings out the action of natural selection.

Evolution by anthropogenic action – Resistance of mosquitoes to pesticides.

When DDT was introduced to control mosquitoes it was tremendously successful. Most of the mosquitoes were sensitive to DDT and were therefore killed. In that population of mosquitoes, few mosquitoes became resistant to DDT and survived. They multiplied and now almost total population of mosquitoes became resistant to DDT.

Same pattern has been observed in bacteria which are multidrug resistant due to excess use of drugs and medicines.

Adaptive Radiation- the process of evolution of different species in given geographical area starting from a point and radiating to other areas of geography (habitat) is called adaptive radiation. Darwin’s finches represent one of the best examples of adaptive radiation. Australian marsupials, each with different from other evolved from one ancestral stock, but all within Australian island continents.

When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats), we can call this convergent evolution e.g Placental mammals and Australian marsupials.

Biological Evolution – the nature select for fittest and fitness is based on characteristics which are inherited. Some organisms are better adopted to survive in otherwise hostile environment. Fitness is the end result of the ability to adopt and get selected by nature.

Lamarck had said that evolution of life form had occurred but driven by use and disuse of organs. He gave the example of giraffe to evolve their neck by foraging leaves on tall trees and had to adapt by elongation of their necks.

Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution .Darwin theory of natural selection was based on certain observations like-

• Limited natural resources.
• Over population
• Competition for resources
• Struggle for existence
• Survival of the fittest.

Mechanism of Evolution

Hugo deVries based on his work on evening primrose brought forth the idea of mutation. Mutation is the large difference arising suddenly in a population.

Mutations are random and directionless while Darwin variations are small and directional. Hugo deVries believed that mutation causes speciation and hence called saltation (single step large mutation).

Difference Amongst Lamarckism, Darwinism and Mutation Theory

Properties	Lamarckism	Darwinism	Mutation Theory
Vital force	The theory believes that every organism has an internal vital force that tends to increase its size upto a certain limit.	Darwinism does not believe in internal vital force.	No internal vital force is involved.
Conscious Reaction	Animals with well developed nervous system react consciously to any change in environments	Darwinism does not involve any conscious reaction.	No conscious reaction is believed to take part in the process of evolution.
Appetency	The theory considers appetency or desires on the part of animals an important force in the development of modifications.	It is not a constituent of the theory.	Appetency in not involved.
Use and Disuse	The organs put to more use are believed to develop more while organs not used begin to degenerate.	The theory is silent about use and disuse of organs.	The theory is silent about it.
Inheritance of Acquired Characters	The characters acquired by an organism during its life are believed to get transferred the next generation.	According to Darwin, all the living cells produce minute particles or pangenesis, which pass into germ cells for transmission to the offspring.	Only those variations are transferred to the offspring which originate in germ cells or in the cells which form germ cells.
Struggle for Existence	The theory does not clearly spell out struggle for existence in relation to high biotic potential.	Organisms produce more offspring than the available food and space so that a struggle for existence ensues amongst them.	The theory believes in the struggle for existence.
Origin of Variations	Variations appear in organisms in response to change in environment, conscious reaction, desire r use and disuse of organs.	Variations appear automatically.	Variations appear due to change in genetic make up.
Continuous Variations	The theory is silent about them though it believes in a continuous modification of organs in a particular direction.	It is based on the origin and selection of continuous variations.	The theory is based on discontinuous variations or mutations.
Natural Selection	The theory does not take into account natural selection or survival of the fittest.	Darwinism is based on natural selection or survival of the fittest.	Mutations theory believes in natural selection or survival of the fittest.
Progress of Evolution	Evolution is a continuous process which moves in a direction governed by environment and appentency.	Evolution is a continuous process, the direction of which is governed by nature.	Evolution is a jerky process, the direction of which is unpredictable though ultimately it is governed by nature.

Hardy- Weinberg Principle- in a given population, frequency of occurrence of alleles or genes can be finding out. These frequencies remains fixed and even remain the same through generation. This fact was represented by Hardy-Weinberg principles using algebraic equation.

This principle states that allele frequencies in a population are stable and is constant from generation to generation. The gene pool remains constant. This is called genetic equilibrium and sum total of all the allelic frequencies is 1.

Binomial expansion of (p+q)2 = p2+2pq+q2=1 where p and q represent the frequency of allele A and allele a in a population . The frequency of AA individuals in a population is simply p2 . This is simply stated in another ways, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p2 . Similarly of aa is q2 , of Aa 2pq. Hence, p2+2pq+q2=1.

When frequency is measured, the actual value varies that indicates the extent of evolutionary changes. Change of frequency in a alleles (Hardy-Weinberg equilibrium) in a population resulted due to evolution.

The factors that affect Hardy-Weinberg equilibrium are-
• Gene migration or gene flow.
• Genetic drift
• Mutation
• Genetic recombination
• Natural selection.

During genetic drift ,sometimes change in alleles frequency is so different in a sample of population that they become a different species. The original drifted population becomes founder and that effect is called founder effect.

Brief Account of evolution

About 2000 million ago first cellular form of life appeared on earth.

• Slowly single-celled organisms became multi-cellular forms and by the time 500 mya, invertebrates were formed and active.
• Jawless fish evolved around 350 mya.
• Organisms started to invade from water to land. Fish with stout and strong fins could move on land and go back to water These animals called lobefins evolved into the first amphibians.
• Later, these amphibians evolved into reptiles. They lay shelled eggs. Then reptiles of different shapes and sizes dominated on earth , fish like reptiles e.g. Ichthyosaurs and the land reptiles e.g dinosaurs. The biggest of them was Tyrannosaurus rex.
• Some of the reptiles evolved into birds and later some of them to mammals. Mammals were viviparous and more intelligent in sensing and avoiding danger .

Class 12 Biology Revision Notes Chapter 6 Molecular Basis of Inheritance

DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are two types of nucleic acid found in living organisms. DNA acts as genetic material in most of the organisms. RNA also acts as genetic material in some organisms as in some viruses and acts as messenger. It functions as adapter, structural, and in some cases as a catalytic molecule

The DNA – it is a long polymer of deoxyribonucleotides. A pair of nucleotide is also known as base pairs. Length of DNA is usually defined as number of nucleotides present in it. Escherichia coli have 4.6 x 106 bp and haploid content of human DNA is 3.3 × 109 bp.

Structure of Polynucleotide Chain

• A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine).

Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine.

A polynucleotide chain

A nitrogenous base is linked to pentose sugar with N-glycosidic linkage to form to form a nucleoside. When phosphate group is linked 5’-OH of a nucleoside through phosphoester linkage nucleotide is formed. Two nucleotides are linked through 3’-5’ phosphodiester linkage to form dinucleotide. More nucleotide joins together to form polynucleotide.

In RNA, nucleotide residue has additional –OH group present at 2’-position in ribose and uracil is found at the place of Thymine.

Structure differences

DNA	RNA
(a) The sugarpresent in DNA is 2-deoxy-D – (-) -ribose.	(a) Thesugar present in RNAis D- (-)- ribose.
(b) DNA contains cytosine and thymine as pyrimidine bases and guanine and adenine is purine bases.	(b) RNA contains cytosine and uracilpyrimidine bones and guanine and adenine as purine bases.
(c) DNA has double strand α-helix structure.	(c) RNA has a single stranded α-helix structure.
(d) DNA molecules are very large their molecular mass may vary from	(d) RNA molecules are comparatively much smaller with molecular mass ranging from 20,000 – 40,000.

Functional differences

(a) DNA has uniqueproperty of replication.	(a) RNA usually does not replicate.
(b) RNA controls the transmission of hereditary effects.	(b) RNA controls the synthesis of proteins.

Double Helix Model for Structure of DNA-James Watson and Francis Crick, based on X-ray diffraction data produced by Wilkin and Rosalind proposed this model of DNA.

The silent features of this model are-

a) DNA is made of two polynucleotide chains in which backbone is made up of sugar-phosphate and bases projected inside it.

b) Two chains have anti-parallel polarity. One 5’à3’ and with 3’à5’.

c) The bases in two strands are paired through H-bonds. Adenine and Thymine forms double hydrogen bond and Guanine and Cytosine forms triple hydrogen bonds.

d) Two chains are coiled in right handed fashion. The pitch of helix is 3.4 nm and roughly 10 bp in each turn.

e) The plane of one base pair stacks over the other in double helix to confer stability.

• Francis Crick proposed the Central dogma in molecular biology, which states that the genetic information flows from DNA —–> RNA ——> Protein.

Packing of DNA helix-

In prokaryotes, well defined nucleus is absent and negatively charged DNA is combined with some positively charged proteins called nucleoids.

In eukaryotes, histones, positively charged protein organized to form 8 molecules unit called histone octomer. Negatively charged DNA is wrapped around the histone octomer to form nucleosome. . Histones are rich in the basic amino acid residues lysines and arginines. Both the amino acid residues carry positive charges in their side chains.

• Single nucleosome contains about 200 base pairs. Chromatin is the repeating unit of nucleosome.

• In nucleus, some region of chromatin are loosely packed (and stains light) and are referred to as euchromatin. The chromatin that is more densely packed and stains dark are called as Heterochromatin. Euchromatin is transcriptionally active chromatin, whereas heterochromatin is inactive.

The search for Genetic Material

Transforming principle – Frederick Griffith in 1928 conducted experiment on bacteria Streptococcus pneumoniae (bacterium responsible for pneumonia). There are two types of strain of this bacteria, some produce smooth shiny colonies (S) and others produce rough colonies(R). Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia.

S strain → Inject into mice → Mice die

R strain → Inject into mice → Mice live

S strain (heat-killed) → Inject into mice → Mice live

S strain (heat-killed) + R strain (live) → Inject into mice → Mice die

Griffith concluded that R strain bacteria have somehow transformed by heat killed S strain bacteria. Some transforming principles transferred from S strain to R strain and enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material.

Biochemical Characterisation of Transforming Principle

• Oswald Avery, Colin MacLeod and Maclyn McCarty worked out to determine the biochemical nature of transforming principle of Griffith.
• They purified biochemicals (proteins, DNA, RNA, etc.) from the heat-killed S cells to see which ones could transform live R cells into S cells. They discovered that DNA alone from S bacteria caused R bacteria to become transformed.So, they concluded that DNA is the genetic material.

Experimental proof that DNA is the genetic material

Alfred Hershey and Martha Chases (1952) worked with virus that infect bacteria called bacteriophages.

• In one preparation, the protein part was made radioactive and in the other, nucleic acid (DNA) was made radioactive. These two phage preparations were allowed to infect the culture of E.coli. Soon after infection, before lysis of cells, the E.coli cells were gently agitated in a blender, to loosen the adhering phage particles and the culture was centrifuged.
• The heavier infected bacterial cells pelleted to the bottom and the lighter viral particles were present in the supernatant. It was found that when bacteriophage containing radioactive DNA was used to infect E.coli, the pellet contained radioactivity.
• If bacteriophage containing radioactive protein coat was used to infect E.coli, the supernatant contained most of the radioactivity.

His experiment shows that protine does not enter the bacterial cell and only DNA is the genetic material.

Properties of Genetic Material:
a) It should be able to generate its replica (replication)
b) It should chemically and structurally be stable.
c) It should provide the scope for slow changes (mutation) that are required for evolution.
d) It should be able to express itself in the form of ‘Mendelian Characters’.

• DNA is chemically less reactive but strcturely more stable as compare to RNA. So, DNA is better genetic material.

• RNA used as genetic material as well as catalyst and more reactive so less stable. Therefore, DNA has evolved from RNA.

Replication of DNA

Watson and Crick suggested that two strands of DNA separate from each other and act as template for synthesis of new complementary strands. After the completion of replication each DNA molecule would have one parental and one newly synthesised strand, this method is called semiconservative replication.

• Messelson and stahl’s shows experimental evidence of semiconservative replication by growing E .coli on nutrient media containing nitrogen salts (15NH4Cl) labeled with radioactive 15N.

• 15N was incorporated into both the strands of DNA and such a DNA was heavier than the DNA obtained from E.coli grown on a medium containing 14N. Then they transferred the E.coli cells on to a medium containing 14N.
• After one generation, when one bacterial cell has multiplied into two, they isolated the DNA and evaluated its density. Its density was intermediate between that of the heavier 15N-DNA and the lighter 14N-DNA.
• This is because during replication, new DNA molecule with one 15N-old strand and a complementary 14N-new strand was formed (semi-conservative replication) and so its density is intermediate between the two.

Replication : Replication of DNA require Enzyme DNA polymerase that catalyse the polymerisation in one strand 5’à3’ only after unwinding with the help of Helicase enzyme . So, replication in one stand is continuous and other strand it is discontinuous to synthesise okazaki fragments that are joined together by enzyme DNA ligase.

Differences between leading and Lagging strands for DNA replication.

Characters	Leading strand	Lagging strand
1. Fragments	It is formed continuously as single fragment.	In the beginning it is formed in the form of small fragments called okazaki segments.
2. RNA primer	It requires only one primer to initiate the growth.	Every fragment requires separate RNA primer to initiate.
3. DNA ligase	Not required.	Required to join DNA fragments.
4. Direction of growth	5’→3’5′→3′	Of complete strand it is 3’→5’3′→5′. However for okazakifragments it is 5’→3’5′→3′ .

Transcription

• It is the process of copying genetic information from one strand of DNA into RNA. In transcription only one segment of DNA and only one strand is copied in RNA. The Adenosine forms base pair with Uracil instead of Thymine.

• Transcription of DNA includes a promoter, the structural gene and a terminator. The strands that has polarity 3’à5 act as template and called template strand and other strand is called coding strand.

Template Stranc	Coding Strand
It is a DNA strand with 3′→→ 5′ Polarity.	DNA Strand with 5′ →→ 3′ Polarity
Acts as template for transcription and codes for RNA	Does not code for any region of RNA during transcription.

Promoter is located at 5’ end and that bind the enzyme RNA polymerase to start transcription. Sigma factor also help in initation of transcription .The terminator is located at 3’end of coding strand and usually defines the end of transcription where rho factor will bind to terminate transcription.

Exons are those sequences that appear in mature and processed RNA. Exons are interrupted by introns. Introns do not appear in mature and processed RNA.

• In eukaryotes, there are three different RNA polymerase enzymes I, II and III, they catalyse the synthesis of all types of RNA.

RNA polymerase I – rRNAs
RNA polymerase II – mRNA
RNA polymerase III – tRNA

The m-RNA provide the template, t-RNA brings the amino acids and read the genetic code, the r-RNA play structural and catalytic role during translation.

DNA Replication	RNA Transcription
Two new molecules of double-stranded DNA are produced.	One new molecule of single-stranded RNA is produced.
Adenine on one strand binds to thymine on the new DNA strand being created.	Adenine on DNA binds to uracil on the new RNA strand being created.
The entire chromosome is replicated.	Only a small portion of the DNA molecule is transcribed to RNA, and this varies based on the cell’s needs at the time.
Enzymes: DNA polymerase	Enzymes: RNA polymerase
Occurs in nucleus.	Occurs in nucleus.

The primary transcript contains both exon and intron and is non-functional. It undergoes the process of splicing in which introns are removed and exons are joined in a defined order.

The hnRNA (heterogeneous nuclear RNA) undergo additional processing called as capping and tailing. In capping in unusual nucleotide (methylguanosine triphosphate) to the 5’end of hnRNA. In tailing polyadenylatelate tail is added at 3’end in a template at independent manner.

Genetic Code : Genetic Code is the relationship of amino acids sequence in a polypeptide and nucleotide/base sequence in mRNA. It directs the sequence of amino acids during synthesis of proteins.

George Gamow suggested that genetic code should be combination of 3 nucleotides to code 20 amino acids.

H.G. Khorana developed chemical method to synthesising RNA molecules with defined combination of bases.

Marshall Nirenberg’s cell free system for protein synthesis finally helped the code to be deciphered.

Salient features of Genetic Code are-

i. The code is triplet. 61 codons code for amino acids and 3 codons do not code for any amino acids called stop codon (UAG, UGA and UAA).

ii. Codon is unambiguous and specific, code for one amino acid.

iii. The code is degenerate. Some amino acids are coded by more than one codon.

iv. The codon is read in mRNA in a contiguous fashion without any punctuation.

v. The codon is nearly universal. AUG has dual functions. It codes for methionine and also act as initiator codon.

Mutations and Genetic code

A change of single base pair (point mutation) in the 6th position of Beta globin chain of Haemoglobin results due to the change of amino acid residue glutamate to valine. These results into diseased condition called sickle cell anaemia.

Insertion and deletion of three or its multiple bases insert or delete one or multiple codons hence one or more amino acids and reading frame remain unaltered from that point onwards. Such mutations are called frame-shift insertion or deletion mutations.

tRNA– the Adapter Molecule

The t-RNA called as adaptor molecules. It has an anticodon loop that has bases complementary to code present on mRNA and also has an amino acid acceptor to which amino acid binds. t-RNA is specific for each amino acids.

The secondary structure of t-RNA is depicted as clover-leaf. In actual structure, the t-RNA is a compact molecule which look like inverted L.

Translation process: Translation is the process of polymerisation of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence of bases in the mRNA. Amino acids are joined by peptide bonds. It involved following steps-

a) Charging of t-RNA.

b) Formation of peptide bonds between two charged tRNA.

• The start codon is AUG. An mRNA has some additional sequence that are not translated called untranslated region (UTR).

• For initiation ribosome binds to mRNA at the start codon. Ribosomes moves from codon to codon along mRNA for elongation of protein chain. At the end release factors binds to the stop codon, terminating the translation and release of polypeptide form ribosome.

Regulation of Gene Expression:

All the genes are not needed constantly. The genes needed only sometimes are called regulatory genes and are made to function only when required and remain non-functional at other times. Such regulated genes, therefore required to be switched ‘on’ or ‘off’ when a particular function is to begin or stop.

The Lac Operon

Lac operon consists of one regulatory gene (i ) and three structural genes (y,z and a). Gene i code for the repressor of the lac operon. The z gene code for beta-galactosidase, that is responsible for hydrolysis of disaccharide, lactose into monomeric units, galactose and glucose. Gene y code for permease, which increases permeability of the cell. Gene a encode for transacetylase.

Lactose is the substrate for enzyme beta-galactosidase and it regulates switching on and off of the operon, so it is called inducer.

Regulation of Lac operon by repressor is referred as negative regulation. Operation of Lac operon is also under the control of positive regulation.

Human Genome Project was launched in 1990 to find out the complete DNA sequence of human genome using genetic engineering technique and bioinformatics to isolate and clone the DNA segment for determining DNA sequence.

Goal of HGP-

a) Identify all the genes (20,000 to 25,000) in human DNA.
b) Determine the sequence of the 3 billion chemical base pairs that make up human DNA.
c) Store this information in data base.
d) Improve tools for data analysis.
e) Transfer related information to other sectors.
f) To address the legal, ethical and social issues that may arise due to project.

• The project was coordinated by the US Department of Energy and the National Institute of health.
• The method involved the two major approaches- first identifying all the genes that express as RNA called Express sequence tags(EST).The second is the sequencing the all set of genome that contained the all the coding and non-coding sequence called sequence Annotation.

Salient features of Human Genome:

a) The human genome contains 3164.7 million nucleotide bases.
b) The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.
c) Less than 2 per cent of the genome codes for proteins.
d) Repeated sequences make up very large portion of the human genome.
e) Repetitive sequences are stretches of DNA sequences that are repeated many times, sometimes hundred to thousand times.
f) Chromosome 1 has most genes (2968), and the Y has the fewest (231).
g) Scientists have identified about 1.4 million locations where single base DNA differences (SNPs – single nucleotide polymorphism) occur in humans.

DNA finger printing is a very quick way to compare the DNA sequence of any two individual. It includes identifying differences in some specific region in DNA sequence called as repetitive DNA because in this region, a small stretch of DNA is repeated many times.

Depending upon the base composition, length of segment and number of repetitive units satellite DNA is classified into many categories.

Polymorphism in DNA sequence is the basis for genetic mapping of human genome as well as fingerprinting.

The technique of fingerprinting was initially developed by Alec Jeffrey. He used a satellite DNA as probe to so high polymorphism was called Variable Number of Tendon Repeats (VNTR).

 Class 12 Biology Revision Notes Chapter 5 Principles of Inheritance and Variation

Genetics is the study of principles and mechanism of heredity and variation. Gregor Johann Mendel is known as ‘father of Genetics’.

• Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity.
• Variation is the degree by which progeny differ from their parents. Variation may be in terms of morphology, physiology, cytology and behavioristic traits of individual belonging to same species.
• Variation arise due to
  • Reshuffling of gene/chromosomes.
  • Crossing over or recombination
  • Mutation and effect of environment.

Mendel’s Law of Inheritance: Mendel conducted hybridization experiments on garden pea (Pisum sativum) for seven years and proposed the law of inheritance in living organisms.

Selection of pea plant: The main reasons for adopting garden pea (Pisum sativum) for experiments by Mendel were –

• Pea has many distinct contrasting characters.
• Life span of pea plant is short.
• Flowers show self-pollination, reproductive whorls being enclosed by corolla.
• It is easy to artificially cross-pollinate the pea flowers. The hybrids thus produced were fertile.

Working method: Mendel’s success was also due to his meticulous planning and method of work –

• He studied only one character at a time.
• He used all available techniques to avoid cross-pollination by undesirable pollen grains.
• He applied mathematics and statistics to analyse the results obtained by him.
• Mendel selected 7 contrasting characters of garden pea for his hybridization experimentsContrasting Characters Studied by Mendel in Pea
  CharacterContrasting character (Dominant/Recessive)Stem heightTall/DwarfFlower colourViolet/WhiteFlower positionAxial/TerminalPod shapeInflated/ConstrictedPod colourGreen/YellowSeed shapeRound/wrinkledSeed colourYellow/Green
• Mendel conducted artificial hybridization/cross pollination using true breeding pea lines. True breeding lines are those that undergo continuous self-pollination and shows stable trait inheritance.
• Hybridization experiment includes emasculation (removal of anther) and transfer of pollen (pollination).

Inheritance of one gene (Monohybrid cross)

Mendel crossed tall and dwarf pea plant and collected all the seeds obtained from this cross. He grew all the seeds to generate plants of first hybrid generation called F1 generation. He observed that all the plants are tall. Similar observation was also found in other pair of traits.

Mendel self-pollinated the F1 plants and found that in F2 generation some plants are also dwarf. The proportion of dwarf plants is 1/4th and tall plants of 3/4th.

• Mendel called the ‘factors’ that passes through gametes from one generation to next generation. Now a day it is called as genes (unit of inheritance).
• Genes that code for a pair of contrasting traits are known as alleles.
• Alphabetical symbols are used to represent each gene, capital letter (TT) for gene expressed in F1 generation and small letter (tt) for other gene.
• Mendel also proposed that in true breeding tall and dwarf variety allelic pair of genes for height is homozygous (TT or tt). TT, Tt or tt are called genotype and tall and dwarf are called phenotype.
• The hybrids which contain alleles which express contrasting traits are called heterozygous (Tt).
• The monohybrid ratio of F2 hybrid is 3:1(phenotypic) and 1:2:1(genotypic).

Test cross is the cross between an individual with dominant trait and a recessive organism in order to know whether the dominant trait is homozygous or heterozygous.

Principle or Law of Inheritance

Based on observations of monohybrid cross, Mendel proposed two law of inheritance-

1. Law of dominance– states that –

a. Characters are controlled by discrete units called factors.
b. Factors always occur in pair.
c. In a dissimilar pair of factors one member of pair dominate the other.

	Dominance	Recessive
(i)	When a factor (allele) expresses itself in the presence or absence of its dominant factor called dominance.	It can only express itself in the absence of or its recessive factor allele.
(ii)	It forms a complete functional enzyme that perfectly express it.	It forms a incomplete defective enzyme which fails to express itself when present with its dominant allele, i.e., in heterozygous condition.

2. Law of Segregation- alleles do not blends and both the characters are recovered during gametes formation as in F2 generation. During gametes formation traits segregate (separate) from each other and passes to different gametes. Homozygous produce similar kinds of gametes but heterozygous produce to different kinds of gametes with different traits.

Incomplete dominance

• It is a post Mendelian discovery. Incomplete dominance is the phenomenon of neither of the two alleles being dominant so that expression in the hybrid is a fine mixture or intermediate between the expressions of two alleles.
• In snapdragon (Mirabilis jalapa), there are two types of pure breeding plants, red flowered and white flowered. On crossing the two, F1 plants possess pink flowers. On selfing them, F2 generation has 1red: 2 pink: 1white. The pink flower is due to incomplete dominance.

Co-dominance

• It is the phenomenon of two alleles lacking dominance-recessive relationship and both expressing themselves in the organism.
• Human beings, ABO blood grouping are controlled by gene I. The gene has three alleles I^A, I^B and i. Any person contains any two of three allele I^A, I^B are dominant over i.
• The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene.
• When I^A and I^B are present together, both express their own types of sugars because of co-dominance.

Incomplete Dominance	Co-Dominance
1.	Effect of one of the two alleles is more conspicuous.	1.	Effect of both the alleles are equally conspicuous.
2.	It produces a mixture of the expression of two alleles.	2.	There is no mixing of the effect of the two alleles.
3.	The F1 does not resemble either of the parents.	3.	The F1 resembles both the parents.
	E.g.: Flower colour in dog flower.		E.g.: ABO blood grouping in humans,

Multiple Alleles

They are multiple forms of a medelian factor or gene which occur on the same gene locus distributed in different organisms in the gene pool with an organism carrying only two alleles and a gamete only one allele. ABO blood grouping also provides a good example of multiple alleles.

Inheritance of Two genes (Dihybrid Cross)

A cross made to study simultaneous inheritance of two pairs of mendelian factors of genes.

Law of independent Assortment – The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.In Dihybrid cross two new combinations, round green & wrinkled yellow are formed due to independent assortment of traits for seed shape i.e round, wrinkled and seed color i.e , yellow and green.

The ratio of 9:3:3:1 can be derived as a combination series of 3 yellow: 1 green, with 3 round : 1 wrinkled. This derivation can be written as follows: (3 Round : 1 Wrinkled) (3 Yellow : 1 Green) = 9 Round, Yellow : 3 Wrinkled, Yellow: 3 Round, Green : 1 Wrinkled, Green

Chromosomal Theory of Inheritance

• Chromosome as well as gene both occurs in pair. The two alleles of a gene pair are located on the same locus on homologous chromosomes.
• Sutton and Boveri argued that the pairing and separation of a pair of chromosomes would lead to segregation of a pair of factors (gene) they carried.
• Sutton united the knowledge of chromosomal segregation with mendelian principles and called it the chromosomal theory of inheritance.

Linkage and Recombination

• When two genes in a Dihybrid cross were situated on same chromosome, the proportion of parental gene combination was much higher than the non-parental type. Morgan attributed this due to the physical association or the linkage of the two genes and coined the linkage to describe the physical association of genes on same chromosome.
• The generation of non-parental gene combination during Dihybrid cross is called recombination. When genes are located on same chromosome, they are tightly linked and show very low recombination.Difference between crossing over and linkage
  Crossing overLinkage1. It leads to separation of linked genes1. keeps the genes together2. It involves exchange of segments between non-sister chromatics of homologous chromosomes.2. It involves individual chromosomes.3. The frequency of crossing over can never exceed 50%.3. The number of linkage group can never be more than haploid Chromosome number.4. It increases variability by forming new gene combinations.4. It reduces variability.

Sex Determination

• Henking in 1891 observed a trace of specific nuclear structure in few insects. He also observed that this specific nuclear structure is located on 50% of sperms only. He called this x body. He was not able to explain its significance.
• Latter it was observed that the ovum that receive the sperms with x body become female and those not becomes males, so this x body was called as sex chromosome and other chromosomes are called autosomes.
• In humans and other organisms XY types of sex determination is seen but in some insects like Drosophila XO type of sex determination is present.
• In both types of sex determination, male produce two different types of gametes either with or without X chromosome or some with X chromosome and some with Y chromosomes. Such types of sex determination are called male heterogamety.
• In birds ZW type of sex determination is present., two different types of gametes are produced by females in terms of sex chromosomes; this type of sex determination is called female heterogamety.
• Sex determination in human beings XY type. Out of 23 pairs of chromosomes, 22 pairs are exactly same in male and female called autosomes. A pair of X chromosome is present in female and XY in male. During spermatogenesis, male produce two type of gametes (sperms), 50% carries Y chromosome and remaining 50% contain X chromosome. Female, produce only one kind of gamete (ovum) having X chromosomes only.
• When sperm having Y chromosome the sex of baby is male and when sperm carrying X chromosome fertilse the egg, the sex of baby is female.

Mutationis a phenomenon which results in alternation of DNA sequence and consequently results in the change in the genotype and phenotype of an organism. The mutations that arise due to due to change in single base pair of DNA are called point mutation e.g Sickle cell anaemia.

Pedigree Analysis

• The analysis of traits in several of generation of a family is called the pedigree analysis. The inheritance of a particular trait is represented in family tree over several generations. It is used to trace the inheritance of particular trait, abnormality and disease.

Genetic Disorders

Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and
Chromosomal disorders.

They are transmitted as the affected individual is sterile.This is always dominant in nature.

Mendelian Disorders	Chromosomal disorders
These are due to alteration in a single gene.	These are caused due to absence or excess of one or more chromosomes or abnormal arrangement of one/more chromosomes.
They are transmitted into generations through Mendelian principles of inheritance.	They may be recessive or dominant in nature.
Examples: Colour blindness Pheffykenonia.	Examples: Downs syndrome, Turner’s syndrome

Medelian disorder includes-

a. Haemophilia- sex linked recessive disease in which, in an infected individual, a minor cut leads to non-stop bleeding. Heterozygous female (carrier) can transmit the disease to their son. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life).

b. Sickle cell anemia- an autosome linked recessive trait in which mutant haemoglobin molecules undergo polymerization under low oxygen tension causing change in shape of the RBC from biconvex disc to elongated sickle like structure. The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG

c. Phenylketonuria- inborn error of metabolism inherited as autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acids phenylalanine to tyrosine . . As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives that results into mental retardation.

Chromosomal Disorders-Failure of segregation of chromatids during cell division results in loss or gain of chromosome called aneuploidy. The failure of cytokinesis leads to two sets of chromosome called polyploidy.

a. Down’s Syndrome– is due to presence of additional copy of the chromosome number 21. The affected individual is short statured with small rounded head, furrowed tongue and partially opened mouth. Mental development is retarded.

b. Klinefleter’s Syndrome– due to presence of an additional copy of X-chromosome (XXY). Such persons have overall masculine development however, the feminine development (development of breast, i.e., Gynaecomastia) is also expressed. They are sterile.

c. Turner’s Syndrome– caused due to the absence of one of the X chromosome. 45 with XO, such females are sterile as ovaries are rudimentary. They lack secondary sexual characters.

Reproductive Health Notes Class 12 Biology Chapter 4

→ According to World Health Organisation (WHO), reproductive health means total well-being in all aspects of reproduction. It includes physical, emotional, behavioral, and social health. A reproductively healthy society has people with normal emotional and behavioral interactions as well as physically and functionally normal reproductive organs.

India has greater proportions of young individuals who belong to different age groups such as adolescents, early childhood, and puberty. Health and education of the younger generation, age of marriage, and childbearing capacity of women are some important areas of concern for the overall reproductive health of the human population.

Reports have revealed that enrolments for secondary school education are low especially for girls, complications during pregnancy, childbirth, and abortions are major reasons for female deaths, the chances of infection of sexually transmitted diseases are maximum between 15 – 24 years.

→ In the world, India was the first country to start action plans and programs to attain total reproductive health at the national level. These programs are called family planning and were started in 1951. Reproductive and Child Health Care (RCH) programs are creating awareness about various reproduction-related areas, providing facilities and support for building a reproductively healthy society.

→ The health centers provide information, guidance, and assistance to mothers before and after delivery. Pregnant women need more nutritious food especially calcium, iron, and vitamins. They should avoid the use of alcohol, drugs, and tobacco because they may cause abnormalities in the developing baby. Women should avoid taking medicines as some may be teratogenic (abnormality causing).

→ These centers also provide safe delivery of the infant and postnatal care. Delivery by untrained midwives may be dangerous so women should prefer delivery in hospitals with trained physicians.

→ The health centers also take care of infant immunization and prophylaxis against anemia and deficiency of vitamins. They should be provided with the following vaccines:

Table: National Immunisation Schedule

Age	Vaccination
3 – 12 Months	DPT – 3 doses at intervals of 4-6 weeks. Polio (oral) – 3 doses at intervals of 4-6 weeks. BCG (intradermal).
9 – 15 Months	The measles vaccine – one dose.
18 – 24 Months	DPT – booster dose. Polio (oral) – booster dose.
5 – 6 Years	DT (bivalent vaccine) against diphtheria and tetanus – booster dose. Typhoid vaccine – 2 doses at an interval of 1-2 months.
10 Years	Tetanus toxoid – booster dose. Typhoid vaccine – booster dose.
16 Years	Tetanus toxoid – booster dose. Typhoid vaccine – booster dose.
Mother during pregnancy	(a) Previously immunized One booster dose of tetanus toxoid 4 weeks before the expected delivery date.(b) Nonimmunised Two doses of tetanus toxoid:  1st between 16-24 weeks and 2nd between 24-32 weeks of pregnancy.

→ These centers train midwives to handle the safe delivery of infants. They also arrange for milk feeding programs. The infants do not have antibodies of their own, they get it from the mother’s milk. Such infants are less prone to allergies than bottle-fed ones.

→ The health centers educate the couples about the importance of small families and proper spacing between successive birth. Too young women are likely to produce underweight and weak babies. To start with pregnancy the reproductive system should be fully mature, physically and functionally as well.

→ Government and non-governmental agencies are working together, using various audio-visual aids to aware people about various programs, infrastructure facilities and to find out new improved methods and to implement them properly.

→ Increased health facilities and better living conditions have increased the population at an alarming level. A rapid decline in death rate, the maternal mortality rate (MMR) and infant mortality rate (IMR), and an increase in the number of people in reproducible age are the main reasons for this. This could lead to a scarcity of basic amenities so serious efforts to check this population growth rate are required.

→ One step to control the population rate is to control the birth rate of the population. To educate and motivate the fertile couples to have smaller families.

→ The regulation of conception by preventive methods or devices to limit the number of off-springs is called birth control. A variety of methods are used for birth control.

→ The birth control methods which prevent fertilization are known as contraception. A contraceptive should be user-friendly, easily available, effective, and reversible with no side effects.

These contraceptive methods are of two main types:
1. Temporary methods: As clear from the name these are temporary measures that are effective for a limited period.
(a) Safe period or Rhythm method: Generally one week before and one week after the menstrual cycle is considered a safe period. This is also called natural family planning. In it, the couples avoid coitus from 10 to 17 days of the menstrual cycle.

It is termed Periodic abstinence. It is based on the observations that ovulation occurs on about the 14th day of the menstrual cycle. An ovum survives for about 1-2 days, sperms remain active for about 3 days. This method reduces the chances of fertilization to 80%.

(b) Coitus Interruptus: This is the oldest method of birth control. It involves the withdrawal of the penis from the vagina by the male before ejaculation so as to avoid insemination. The drawbacks of this method are that the male produces some lubricating fluid from Cowper’s glands which contains many sperms. A lapse of timing may result in late withdrawal and therefore pregnancy.

(c) Lactational Amenorrhea: This means the absence of menstruation. It is based on the fact that ovulation does not occur during intense lactation after parturition, so there is no menstrual! cycle. The chances of conception are nil. This method does not have any side effects. It can only be effective for a maximum of six months after parturition.

(d) Chemical methods: These include jellies, foam tablets, pastes, or creams that contain spermicides (agents to kill sperms) such as lactic acid, boric acid, citric acid, zinc sulfate, or potassium permanganate. Before intercourse, if these are introduced into the vagina, they adhere to the mucous membrane and kill the sperms.

(e) Mechanical means: These are barrier methods that prevent the sperms and ovum to come closer.

They are of three types:
1. Condom (Nirodh) is made up of a thin rubber/latex sheath meant to cover the penis so that semen would not enter into the female reproductive system. The female condom covers the vagina and cervix, just before coitus. These should be discarded after a single-use. Their use is simple and has no side effects. These are very useful against STDs and AIDS.

2. Diaphragm and cervical cap: These are the rubber plastic covers that are fitted on the cervix in a female’s vagina and blocks the entry of sperms through the cervix. These are reusable and must be kept fit for at least six hours after intercourse. Every time these are smeared with spermicidal jelly, creams, or foams to increase their contraceptive efficiency.

3. Intrauterine Devices (IUDs): These are metal or plastic objects inserted inside the uterus of the female. These may be non-medicated lUD’s such as Lippes Loop, Copper releasing IUDs e.g. CuT, Cu7, Multiload 375, and the hormone-releasing ones e.g. Progestasert. LNG-20.

They prevent the fertilization of egg or embryo implantation. IUDs increase phagocytosis of sperms within the uterus, Cu²⁺ ions released by some of them suppress sperm motility and their fertilizing capacity. The hormone-releasing IUDs make the uterus unsuitable for implantation and cervix, hostile to the sperms. These should be used with the help of a physician. Their presence may act as a minor irritant.

Their drawbacks are spontaneous expulsion, occasional hemorrhage, perforation of the uterus, or tubal pregnancy.
1. Physiological (Oral) devices: These are birth control pills that check ovulation by inhibiting the secretion of follicle-stimulating hormone and luteinizing hormone. A combined pill is widely used, it contains progesterone and estrogen in high doses to prevent ovulation.

→ Pill Mala D is taken daily, and pill Saheli is taken weekly, it contains a non-steroidal preparation called ‘Centchroman’. These have side effects like nausea, breast tenderness, weight gain, slight bleeding, and high blood pressure. They also reduce certain types of cancer.

→ Progestagen along with estrogen is used by females as injections or implants under the skin. Their action is similar to pills and is for a longer duration (3 to 4 years).

→ Progestagens if taken within 72 hours of coitus are very effective and can avoid pregnancy due to some accidents.

2. Permanent Method: These are surgical methods or sterilization, which provides a permanent or terminal method for birth control. In males, it is called vasectomy and in females, it is called tubectomy. Surgical methods block gamete transport and thus prevent pregnancy. In a vasectomy, a small part of the vas deferens is removed or tied up by a small incision on the scrotum.

In tubectomy, a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through the vagina. This is done under local anesthesia and does not affect the normal sex life. These techniques are highly effective and widely used but they have poor reversibility.

→ Laparoscopy: A small laparoscope (telescopic instrument) is used in tubal ligation. It blocks the fallopian tubes. Thus the eggs fail to pass the fallopian tube and sperms fail to reach the eggs.

→ Sterilization is the most effective measure for birth control. All these methods should be used under the guidance of a medical practitioner.

→ Voluntary Termination of Pregnancy or Medical Termination of Pregnancy (MTP) is known as abortion. The pregnancy is terminated before the fetus becomes viable. It is a method of fertility control used all over the world. Certain pills induce menstruation which acts as abortions and checks the implantation of a zygote or detaches the implanted egg. MTPs if done during the first 12 weeks of pregnancy is safe. It becomes riskier during the second trimester. Only a certified practitioner should be contacted for MTP.

Contraception methods

→ RU – 486 is an analog of progesterone that terminates pregnancy within the first few weeks. It acts by blocking the receptors in the uterus thus preventing progesterone from maintaining pregnancy.

→ Infections or diseases that transmit through unsafe sexual intercourse are called sexually transmitted diseases (STDs) or reproductive tract infections (RTI) or Venereal diseases (VD) Gonorrhoea and syphilis are the most common. Another is AIDS. Adolescents are more vulnerable to these because of a lack of proper knowledge.

Table: Common STDs and their causative agents

Infection/Disease	Causative agent
Gonorrhea	Neisseria gonorrhoeae
Syphilis	Treponema pallidum
Chlamydiosis	Chiarnydia trachomatis
Genital Herpes	Herpes Simplex Virus. Human Papilloma Virus
Hepatitis-B	Hepatitis Virus
HIV-AIDS	Human Immunodeficiency virus
Trichomoniasis	Trichomonas vaginal is/Protozoan

→ To avoid these one should avoid having sex with unknown partners or multiple partners, always use condoms during coitus and seek medical help as soon as possible.

→ Early symptoms of most of these infections are minor. It includes slight itching, fluid discharge, slight pain or swelling in the genital region. If not paid proper attention these may become complicated ones as pelvic inflammatory disease (PID), abortions, ectopic pregnancy, stillbirth, infertility, or even cancer of the reproductive tract.

→ Infertility is the condition when couples are unable to produce children in spite of unprotected sexual cohabitation. Infertility may be physical, congenital, diseases, drugs, immunological, or even psychological. These problems can be cured by assisted reproductive technologies (ART). In vitro fertilization (IVF) is done followed by Embryo transfer (ET)is one of such practices done to cure infertility.

In IVF, ova from the donor female and sperms from the donor male are collected and induced to form a zygote, which is then transferred into the fallopian tube known as ZIFT-zygote intrafallopian transfer. For ZIFT the embryos are up to 8 blastomeres. Embryos with more than 8 blastomeres are transferred into the uterus called JUT (intrauterine transfer) for further complete development.

GIFT: gamete intrafallopian transfer, is the transfer of ovum from a donor to the receiver female who cannot produce one. Intracytoplasmic sperm injection (ICSI) is a product where embryos are produced in the laboratory. The artificial insemination (AI) technique is used in case of male’s sperm count is low. In IUT: intrauterine insemination, semen is collected from donors and artificially introduced into the vagina or uterus.

→ Polyovulation: Discharge of several ova in one ovulatory cycle.

→ Hygienist: A person well versed in the principles of hygiene.

→ Laparoscopy: Examination of the peritoneal cavity through an incision in the abdominal wall.

→ Abortion: Giving birth to an embryo or fetus prior to the stage of viability at about 20 weeks of gestation.

→ Premature birth: Birth after the age of fetal viability but before full term.

→ Fetus: Developing young one from the end of the eight weeks to the moment of birth.

→ Foeticide: Destruction of embryo or fetus in the uterus.

→ RCH programs: Reproductive and Child Health Care program.

→ IUDs: Intra-Uterine Devices.

→ MTP: Medical termination of pregnancy.

→ VD: Venereal diseases.

→ RTI: Reproductive tract infections.

→ PID: Pelvic inflammatory diseases.

→ ART: Assisted reproductive technologies.

→ IVF: Invitro fertilization.

→ ET: Embryo transfer.

→ ZIFT: Zygote intrafallopian transfer.

→ IUT: Intra uterine transfer. .

→ GIFT: Gamete intrafallopian transfer.

→ ICSI: Intracytoplasmic sperm injection.

→ AI: Artificial insemination.

→ IUI: Intra-uterine insemination.

Class 12 Biology Revision Notes Chapter 3 Human Reproduction

Humans are sexually reproducing and viviparous. The reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms in males and ovum in females, transfer of sperms into the female genital tract (insemination) and fusion of male and female gametes (fertilisation) leading to formation of zygote. This is followed by formation and development of blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation) and delivery of the baby (parturition)

The Male Reproductive System: It cChapteronsists of:

a) Primary sex organs i.e. a pair of testes suspended in a scrotum.

b) Secondary sex organs i.e. a pair of ducts each differentiated into rete testis, vasa efferentia, epididymis and vas deferens, ejaculatory duct and the associated glands

c)  External genitalia

• The testes are situated outside the abdominal cavity in a pouch called scrotum, which help in maintaining the low temperature of testes necessary for spermatogenesis.
• Each testes has about 250 testicular lobules and each lobule contain highly coiled seminiferous tubules in which sperms are produced. Each seminiferous tubules is lined by two types of cells, spermatogonia ( male germ cell) and Sertoli cells.
• Leydig cells or interstitial cells present around the seminiferous tubules synthesize and secrete androgen hormone.

• Ejaculatory duct store and transport the sperm from testes to outside through urethra which originate from urinary bladder and extend through penis to its external opening urethral meatus.
• The penis is male external genitalia. The enlarged end of penis is called the glans penis is covered by a loose fold of skin called foreskin.
• Male accessary glands include paired seminal vesicles, prostrate and paired bulbourethral glands. Secretion of these glands forms the seminal plasma which contains fructose, calcium and enzymes. The secretion of bulbourethral glands also helps in lubrication of the penis.

The Female Reproductive System: It consists of :

a)The primary sex organ that is a pair of ovaries

b)Secondary sex organs- the duct system consisting of a pair of fallopian tube , a uterus , cervix and vagina

c)External genitalia

d)Mammary glands

• Ovaries are primary female sex organ that produce the female gamete and several steroid hormones. Each ovary is covered by thin epithelium which encloses the ovarian stroma, which is divided into a peripheral cortex and an inner medulla.
• Fallopian tube extends from periphery of ovary to the uterus. The part closer to ovary is a funnel shaped structure called infundibulum having finger like projection called fimbriae.
• Infundibulum leads to ampulla and join with uterus with isthmus. Uterus is pear shaped structure also called womb.
• Uterus open vagina through a narrow cervix. The cavity of cervix (cervical canal) along with vagina forms the birth canal.
• The wall of uterus has three layers of tissue:

I. Perimetrium- external membrane.

II. Myometrium – middle thick layer of smooth muscles which exhibit strong contraction during delivery of baby.

III. Endometrium – line the uterine wall and undergo cyclic changes during menstrual cycle.

Female external genitalia includes

• Mons pubis – cushion of fatty tissues covered by skin and pubic hair.
• Labia majora- fleshy fold that surround the vaginal opening.
• Labia manora – paired fold of tissue under labia majora.
• The opening of vagina is often partially covered by a membrane called hymen. The tiny finger like projection present at the upper junction of two labia manora above the urethral opening is called clitoris.

Mammary glands are paired structures that contain glandular tissues and variable fats. Each glandular tissue contains 15-20 mammary lobes containing alveoli that secrete milk. Mammary ducts join to form mammary ampulla.

Gametogenesis: The process of formation of male and female gametes in testes and ovary respectively is called gametogenesis.It is of two types:
1. Spermatogenesis in males
2. Oogenesis in females

Spermatogenesis- in testes immature, male germ cells (spermatogonia) produce sperm by spermatogenesis that begin at puberty.

• The spermatogonia present at the inner side of seminiferous tubules multiply by mitotic division and increase in number. Each spematogonium contain 46 chromosomes.
• Spermatogonia forms spermatocyte that undergo meiotic division to reproduce secondary spermatocytes having 23 chromosomes.
• The spermatids are transformed into spermatozoa by the process called spermiogenesis. The sperm heads remain embedded in sertoli cells and are released from seminiferous tubules by the process of spermiation.

Hormonal control of spermatogenesis

• Spermatogenesis initiated due to increase in secretion of gonadotropin releasing hormone by hypothalamus
• Increase in GnRH act on anterior pituitary and stimulate secretion of two gonadotropins, LH and FSH
• LH acts on Leydig cells and stimulates them to secrete androgens.
• FSH acts on Sertoli cells, stimulates secretion of some factors which help in spermiogenesis

Structure of sperm- sperm is a microscopic structure composed of a head, neck, a middle piece and a tail. The sperm head contain elongated haploid nucleus, anterior portion of which is covered by cap like structure acrosome.

Human male ejaculates about 200-300 million sperms during a coitus. The seminal plasma along with the sperms constitutes the semen. The function of male sex secondary ducts and glands are maintained by androgen hormones.

Oogenesis : The process of formation of mature female gametes is called oogenesis. It started during embryonic development stage when millions of ogonia (gamete mother cells) are formed in each fetal ovary.

• The gametes mother cells start division and enter into prophase-I of meiotic division and get temporally arrested at that stage called primary oocytes.
• Each primary oocyteget surrounded by a layer of granulosa cell than it is called the primary follicle.
• At puberty, about 60,000- 80,000 primary follicles are left in each ovary.

• Primary follicle gets surrounded by more layers of granulosa cells called secondary follicle that transform into tertiary follicle that contain fluid filled cavity called antrum.

• The tertiary follicles further changes into the mature follicle called Graafian follicle, which rapture to release secondary oocytes (ovum) from the ovary by the process of ovulation.

Menstrual cycle: The reproductive cycles in female primates is called menstrual cycle. It start at puberty and is called menarche.

Phases of Menstrual Cycle

The menstrual cycle consists of following four phases:

(1) Menstrual Phase:

(i) In a 28 days menstrual cycle,the menses  takes place on cycle days 3-5.

(ii) The production of LH from the anterior lobe of the pituitary gland is reduced.

(iii) The withdrawal of  this hormone causes degeneration of the corpus luteum and, therefore progestrone production is reduced.

(iv) Production of oestrogen is also reduced in this phase.

(v) The endometrium of uterus breaks down & menstruation begins.

(vi) The cells of endometrium secretions, blood & unfertilised ovum constitutes the menstrual flow.

(2) Follicular Phase:

(i) This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.

(ii) The follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.

(iii) Oestrogen stimulates the proliferation of the endometrium of the uterine wall.

(iv) The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.

(3) Ovulatory Phase:

(i) Both LH & FSH attain a peak level in the middle of cycle (about 14^th day).

(ii) Oestrogen concentration in blood increases.

(iii) Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum.

(iv) In fact LH causes ovulation.

(4) Luteal Phase:

(i) Includes cycle days 15 to 28.

(ii) Corpus luteum secretes progestrone.

(iii) Endometrium thickens.

(iv) Uterine glands become secretory.

Hormonal Control of MC

(i) FSH stimulates the ovarian follicles to produce oestrogens.

(ii) LH stimulates corpus luteum to secrete progestrone.

(iii) Menstrual phase is caused by the increased production of oestrogens.

(iv) LH causes ovulation

(v) Proliferative phase is caused by the increased production of oestrogens.

(vi) Secretory phase is caused by increased production of progestrone.

Fertilisation and Implantation

The process of fusion of sperm with ovum is called fertilisation.

• During coitus (copulation) semen is released into vagina. The motile sperms swim rapidly to reach the junction of isthmus and ampulla of fallopian tube. The ovum also reaches there and fusion of gametes takes place in at ampullary-isthmic junction.
• In this acrosome of sperm undergoes acrosomal reaction and releases certain sperm lysins which dissolve the egg envelopes locally and make the path for the penetration of sperm.
• These sperm lysins contain a lysing enzyme hyaluronidase which dissolves the hyaluronic acid polymers in the intercellular spaces which holds the granulosa cells of corona radiata together; corona penetrating enzyme (that dissolves the corona radiata) and acrosin (which dissolves the zona pellucida). Then it dissolves the zona pellucida.

Cortical reaction:

(a) Immediately after the entry of a sperm into the egg, the later shows a cortical reaction to check the entry of more sperms.

(b) In this reaction, the cortical granules present beneath the egg’s plasma membrane release chemical substance between the ooplasm and the plasma membrane (vitelline membrane).

(c) These substances raise the vitelline membrane above the egg surface. The elevated vitelline membrane is called fertilization membrane.

(d) The increased space between the ooplasm and the fertilization membrane and the chemical present in it effectively check the entry of other sperm.

(e) If polyspermy occurs, that is more than one sperm enter the secondary oocyte, the resulting cell has too much genetic material to develop normally

• The haploid gametes fuse together to form diploid zygote. As the zygote moves towards the uterus, the mitotic division starts and form cleavage to change into 2, 4,8,16 celled blastomeres.
• The blastomeres with 8 to 16 cells are called morula. Morula divide to change into blastocysts .The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass.The outer layer of blastocyst is called trophoblast that attach with endometrium of uterus, called implantation that leads to pregnancy.

Pregnancy and embryonic development

The finger-like projections on trophoblaste after implantation called is called chronic villi that along with uterine wall forms functional unit between developing embryo and maternal body called placenta. Placenta is attached with fetus with an umbilical cord that transport food and oxygen to embryo.

• Hormones hCG (human chorionic gonadotropin), hPL (human placental lactogen) and relaxin are produced in woman only during pregnancy by placenta.
• After implantation, the inner cell mass (embryo) differentiates into an outer layer called ectoderm and an inner layer called endoderm. A mesoderm soon appears between the ectoderm and the endoderm. These three layers give rise to all tissues (organs) in adults. It is important to note that the inner cell mass contains certain cells called stem cells which have the potency to give rise to all the tissues and organs
• In human, after one month of pregnancy the embryo’s heart is formed. By the end of 2^nd month limbs and digits are formed. By the end of 12 months, major organs and external genital organs are well developed. The first movement of foetus is observed in 5 months. By the end of 24 weeks body is covered with fine hair, eye lids and eyeless are formed. At the end of 9 months fetus is fully developed.

PARTURITION AND LACTATION

Parturition-the process of delivery of fully developed foetus is called parturition.

• Signals for parturition originate from the fully developed fetus and placenta inducing mild uterine contractions called Foetal ejection reflex
• It triggers the release of oxytocin from maternal pituitary

The mammary glands of female, start producing milk, to the end of pregnancy by the process of lactation. The milk produced during the initial few days of lactation is called colostrum, which contain several antibodies.