a) Taq polymerase enzyme is obtained from the bacterium Thermophilous aquaticus. This enzyme is active at high temperature. It is used to denature DNA at temperature of about 94°C during DNA amplification by polymerase chain reaction (PCR).
(b) ADA = Adenosine deaminase The deficiency of this enzyme results in production of functional lymphocytes. It cause SCID (Severe Combined Immunodeficiency.)
(c) Gene Therapy. 1. It involves the delivery of a normal gene into individual or embryo to replace the defective mutant alleles.
2. The first gene therapy was given in 1990to a four year old girl with deficiencyofADA.
3. It is cured by bone marrow transplantation in some children but it is not completely curable.
4. In this case a functional ADA, cDNA (using a retroviral vector) is introduced into lymphocytes, such lymphocytes are introduced back into blood of patient.
5. The patient requires infusion of such genetically engineered lymphocytes.
6. If a functional gene is introduced into bone marrow at early stages of embryonic development, it would be a permanent cure.

Hazards of Transgenic Animals.
1. Proteins. Genes introduced in various organisms operate through synthesis of polypeptide proteins and enzymes. However, foreign proteins are generally attacked by the defence system resulting in damaged biochemicals which may prove harmful and in the long term produce allergy.
2. Human organs. Replaceable human organs like kidneys, liver, heart, pancreas etc. can be obtained only from auto grafts and isografts. Will it be ethical to grow human body, human body organs for obtaining the required organs.
3. Human cloning. This can solve the problem of infertility. However, such a method of human reproduction will destroy family system, fine human feelings and fabric of human society.
4. Recreation. It is not only a fancy but also desire of numerous children, adults and the elders to see live dinosaurs.

(i) Restriction Endonucleases.
(ii) Gel Electrophoresis.
(iii) T4 ligase.
(iv) Vector and competant host
(v) DNA delivery system.

Following are the advantages of recombinant Insulin:
(a) Recombinant Insulin can be prepared on a large scale without worrying about the source animal.
(b) Batch to batch consistency can be maintained, and quality can be maintained.
(c) Helps in preventing cruelty against animals.
(d) Chances of allergic reactions have been minimized.
(e) Chances of transmission of infection from source animals have been nullified.
(f) Recombinant Insulin has almost replaced animal-sourced Insulin from around the world.
(g) This paves the way for forms of Insulin, which need not be given through injections.

Transgenic animals Transgenic animals are produced for the following purposes:
(i) Transgenic animals are designed to allow the study of how genes are regulated and how they affect the normal functions of the body and its developments e.g. Information is obtained as to how insulin has a role as growth factor.
(ii) Transgenic animals are designed to increase our understanding as to how genes control the development of diseases; they serve as models for human di eases.
(iii) Transgenic animals that produce useful biological compounds lure created by introducing a portion of the DNA that codes for that product, e.g.
\(\alpha \) -I antitrypsin is produced for curing emphysema.
(iv) Transgenic mice are being developed to test the safety of vaccines. e.g., polio vaccine has been tested on mice.

(i) Options to increase food supply:
Agro-chemical based agriculture, using chemical fertilizers and pesticides.
Organic agriculture, using biofertilizers, biopesticides, vermi composting, etc.
Genetically-engineered (GM) crops based agriculture.
(ii) The success of Green Revolution was due to Use of improved/hybrid crop varieties  Better management practices.
Use of agrochemicals (pesticides and fertilisers).
(iii) We still search for other methods for the following reasons:
The agrochemicals cause pollution of soil and water and reduce the yield in the long run; they are too expensive for the farmers. Further increase in the yield of the existing varieties by conventional breeding is not possible.

Gene therapy is a collection of methods, that allows correction or replacement of a defective gene.
Correction of a genetic defect involves delivery of a normal gene into the individual's embryo to take over the function of the non-functional gene.
ADA (Adenosine deaminase) deficiency was treated in a 4 year old girl.
This disorder is caused by the deletion of the gene for the enzyme.
The lymphocytes from the blood of the patient are grown in a culture in vitro.
A functional ADA cDNA (using retroviral vector) is introduced into lymphocytes; such lymphocytes are introduced back into the blood of the patient.
But the patient requires periodic infusion of such genetically-engineered lymphocytes.
 If the gene isolated from marrow cells is introduced in cells in the early stage, it could be a permanent cure.

Advantages:
(i) Genetic modification has made the crops more tolerant to abiotic stresses like cold, heat, drought, salinity, etc.
(ii) It has reduced the dependence of crops on chemical pesticides as they are made pest-resistant.
(iii) Post-harvest losses are much reduced.
(iv) As the plants have increased efficiency of mineral usage by plants, the early exhaustion of fertility of soil is prevented.
(v) Food produced from GM (Genetically Modified) crops has enhanced nutritional value.
(vi Genetic modification has been used to create tailor-made plants to supply resources to industries such as starch, fuels, pharmaceuticals, etc.
Disadvantages:
The proteins produced by the GMO may cause allergy and other problems.
The genes present in the transgenic organisms may transform our intestinal bacteria also resistant to certain antibiotics.
When the resistant gene is transferred through pollen to the weeds, they may also become resistant to such pests and start flourishing.