Practical Applications of Genetic Engineering

1. Diagnosis of Diseases. Genetic as well as infectious diseases can be diagnosed by using DNA technology. This is done with probe consisting of a short segment of single-stranded DNA attached to a radioactive or fluorescent marker. This method is used these days to identify causative agents such as Salmonella of food poisoning, Staphylococcus of pus formation, HIV of AIDS, virus of hepatitis B, etc.

2. Gene Therapy. Genetic engineering may one day enable the medical scientists to add, delete or alter a specific gene to modify the patient's genotype for the treatment of hereditary diseases (haemophilia, phenylketonurea). This new system of medicine is called gene therapy.

The genetic diseases being investigated for gene therapy range from sickle- cell anaemia to severe combined immuno-deficiency (SCID). The SCID patient has a

defective gene for the enzyme adenosine deaminase (ADA). He lacks functional T-lymphocytes and, therefore, fails to combat the infecting pathogens. Lymphocytes are extracted from the patient's bone marrow and a normal functional copy of human gene coding for ADA is introduced into these lym­phocytes with the help of a retrovirus. The cells so treated are reintroduced into the patient's bone marrow. The lymphocytes produced by these cells contain functional ADA gene, and reactivate the victim's immune system for life.

Cancer cells lack functional tumour-suppres­sor genes which code for proteins that restrain the growth of normal cells. A cancer cell should change to non-malignant state if a wild-type tumour-sup­pressor gene, such as p53, is introduced into it. The p53 gene can be delivered to tumour cells through the infection with a virus that has been engineered to carry this gene. The p53- bearing viruses have been shown to restore normal growth to malignant cells both in culture and laboratory animals. The technique has not yet succeeded in humans.

3. Production of Genetically Modified Microorganisms. Many microorganisms have been genetically engineered for a variety of purposes

a) Synthesis of Pharmaceutically Useful Chemicals. These include human insulin (in E. coli), interferons, human growth hormone, blood clotting factor VIII/IX, tissue plasminogen ac­tivator that dissolves clots, vaccines, antibodies, etc.

b) Efficient Nitrogen Fixation. Bacterium Rhizobium meliloti is used as a biofertilizer.

c) Depollution of Environment. Bacterium Pseudomonas is used to purify the environment. It accumulates heavy metals (copper, lead) from the environment and incorporates them into com­pounds (copper sulphate, lead sulphate) which are readily recoverable. The process is called bioremediation.

d) Crop Protection. Fungus Trichoderma is employed in biocontrol against plant diseases and pests.

e) Penicillin Production. High-yielding strains of the fungus Penicillium are producing penicillin in large amounts.

f) Lignin Removal. Trametes is used for removal of underisable lignin in wood industry.

g) Synthesis of Useful Substances. Bacteria are used as living laboratories for synthesis of en­zymes and vitamins on large scale.

h) Insect Control. Bacillus thuriengiensis produces endotoxins used for insect control.

i) Control of Fungal Diseases. Many fungi produce chitinases that are used for the control of fungal diseases.

j) Increased Milk and Beef Yield. Milch cows are injected with bovine growth hormone (BGH), made by E. coli, to raise milk production. BGH also improves beef yield in cattle.

k)) Digestion of Cellulose in Animal Fodder. An enzyme cellulase prepared by engineered E. coli is given to animals for digestion of entire food.

4. Production of Transgenic Plants. Or­ganism containing a foreign gene from a different species received by genetic engineering is called transgenic organism. Some transgenic plants having useful characters have been formed by genetic engineering (tomato, soybean, cotton, corn, potato, rice, tobacco).

5. Production of Transgenic Animals. Certain animals after receiving foreign genes produce high­ly valuable materials. They can be used as bioreactors to get such substances. Transgenic sheep produce clotting factor for haemophiliacs. Trans­genic goats produce a protein which can dissolve blood clots - a treatment for coronary thrombosis. There are transgenic sheep that yield more wool. Transgeric cattle, hogs, sheep and fish grow far quickly and produce more meat.

6. Help in Understanding Biological Proces­ses. Genetic engineering assists in ascertaining mechanism of differentiation and ageing, gene ex­pression and mapping of genes in chromosomes. The concepts of (i) exons and introns, and (ii) regulatory genes have been revealed by genetic en­gineering.

7. Solution of Disputed Parentage. Disputed parentage can be more accurately solved by recom­binant technology than by blood tests.

8. Genetic Counselling. Prospective parents, who are carriers of genetic disorders, can be advised about the possibility of the inheritance of the disor­der by their children. This is done by determining the genotypes of the parents.