Animals whose DNA is manipulated to possess and express an extra (foreign)...
Animals whose DNA is manipulated to possess and express an extra (foreign) gene are known as transgenic animals.
Transgenic rats, rabbits, pigs, sheep and cows have been produced.
Following are the common reasons for developing transgenic animals:
i. Study of normal physiology and development
Transgenic animals are useful to study gene regulation, their effect on the normal functions of the body and its development.
For example, study of complex growth factors like insulin-like growth factor.
ii. Study of disease
Study of genes which are responsible for diseases in human and their treatment.
Transgenic models have been developed for many human diseases like cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease.
iii. Biological products
Useful biological products can be produced by introducing, into transgenic animals, the portion of DNA (or genes) which codes for a particular product.
For example, human protein (α-1-antitrypsin) is used to treat emphysema.
In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk (2.4 g/L).
The milk contained the human alpha-lactalbumin and was more nutritionally balanced for
human babies than natural cow milk.
iv. Vaccine safety
Transgenic mice are developed to test safety of vaccines, before being used on humans.
For example, transgenic animals are being used to test the safety ofthe polio vaccine.
Mice could replace the use of monkeys to test the safety of the vaccine.
v. Chemical safety testing
Transgenic animals are made to carry genes, which make them more sensitive to the toxic substances than non-transgenic animals.
On exposing to the toxic substances, their effects are studied in less time.