Transgenic animals are those in whom the DNA is manipulated to possess and express an extra gene. Transgenic animals are specifically designed to allow the study of gene expressions, gene regulation and how genes affect normal function and development of the body. The commonly produced transgenic animals are rats, rabbits, sheep, pigs, fishes and cows. But out of these almost 95% transgenic animals are mice. Transgenic animals can be used to study normal physiology and development, disease, biological products, vaccine safety, chemical safety testing.