Animals that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals.

Following are the four main areas where they can be utilised

(i) To Study Normal Physiology and Development

These animals can be used to study that which factor/gene products are needed at what time of development. By the expression of certain genes, they help scientists to understand the normal gene expression at various stages of growth and development.

(ii) Study of Diseases

Transgenic animals can be created to serve as models for various human diseases. They also help us to understand the involvement of various genes in diseases like cancer, Parkinson' disease etc.

(iii) Vaccine Safety

Transgenic animals can be used to test vaccines like polio vaccine. Transgenic mice have shown promising results in this area and would replace the vaccine testing on monkeys in the years to come.

(iv) Chemical Safety Testing

Transgenic animals are created which are more sensitive to certain chemicals/drugs. These are used to study the toxicity or side effects of that chemical/drug. The advantage is that we get results faster.

After identifying a useful gene in bacteria, following steps should be followed

(i) Isolation of useful gene using restriction endonucleases

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(ii) Transferring the gene to a suitable vector to create a recombinant DNA molecule

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(iii) Transfer of these recombinant DNA molecules to the target cells.

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(iv) Screening of cells for transformation

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(v) Selection of transformed cells

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(vi) Regeneration of plants from the transformed cells to get transgenic plants.

Biotechnology has influenced our lives in the following ways

(i) It has provided us with genetically modified crops of better quality and high nutritive value.

(ii) It has made better and safer recombinant vaccines available to the human.

(iii) It has helped to develop transgenic animals that can produce human proteins.

(iv) It has enabled the cure of genetic diseases using gene therapy.

(v) Environment pollution has also been taken care of with the help of genetically engineered microbes.

Genetically modified plants have been useful in many ways as follows

(i) These plants are more tolerant to abiotic stresses (cold, drought, salt, heat).

(ii) They have reduced the reliance on chemical pesticides (pest-resistant crops).

(iii) They helped to reduce post harvest losses.

(iv) They increases the efficiency of mineral usage by plants (this prevents early exhaustion of fertility of soil).

(v) Enhanced nutritional value of food, e.g., vitamin-A enriched rice.

In addition to these uses, GM plants have been used to create tailor-made plants to supply alternative resources to industries, in the form of starches, fuels and pharmaceuticals.

(a) Genetically modified plants can reduce the usage of chemical pesticides by introducing pest resistant plants.

e.g., There are several nematodes that parasitie, a wide variety of plants and animals including human beings. A nematode Meloidogyne incognita infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi).

Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant. The introduction of DNA was such that it produced both sense and antisense RNA in the host cells.

These two RNA's being complementary to each other formed a double stranded RNA that initiated RNAi and thus, silenced the specific mRNA of the nematode. The consequence was that the parasite could not survive in a transgenic host expressing specific interfering RNA.

(b) Genetically modified plants can enhance nutritional value of food crops.

e.g., 'Golden rice' developed at Swiss Federal Institute of technology is an example of nutritionally modified crop. It is rich in vitamin-A ( $\beta$-carotene). The rice grains are golden-yellow in colour. It contains 'beta-carotene' gene from daffodil plant and also from some bacteria. Golden rice can prevent child blindness which is caused due to the deficiency of vitamin-A.