Define transgenic animals. Explain in detail any four areas where they can be utilised.

(N/A) $(i)$ $\text{Normal physiology and development:}$ Transgenic animals are specifically designed to allow the study of how genes are regulated and how they affect the normal functions of the body and its development. For example,studying complex factors involved in growth,such as insulin-like growth factor. By introducing genes from other species that alter the formation of this factor and studying the resulting biological effects,information is obtained about the biological role of the factor in the body.
$(ii)$ $\text{Study of disease:}$ Many transgenic animals are designed to increase our understanding of how genes contribute to the development of diseases. These are specially made to serve as models for human diseases so that investigation of new treatments becomes possible. Today,transgenic models exist for many human diseases such as cancer,cystic fibrosis,rheumatoid arthritis,and Alzheimer's.
$(iii)$ $\text{Biological products:}$ Medicines required to treat certain human diseases can contain biological products,which are often expensive to produce. Transgenic animals that produce useful biological products can be created by the introduction of the portion of $DNA$ (or genes) which codes for a particular product,such as human protein ($\alpha-1$-antitrypsin) used to treat emphysema. Similar attempts are being made for the treatment of phenylketonuria $(PKU)$ and cystic fibrosis. In $1997$,the first transgenic cow,Rosie,produced human protein-enriched milk $(2.4 \text{ g/L})$. The milk contained human alpha-lactalbumin and was nutritionally a more balanced product for human babies than natural cow milk.
$(iv)$ $\text{Vaccine safety:}$ Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humans. Transgenic mice are currently used to test the safety of the polio vaccine. If successful and found to be reliable,they could replace the use of monkeys to test the safety of vaccine batches.