Basic principle of developing transgenic plants and animals is to introduce the gene of interest into nucleus of-
A. Somatic cell
B. Vegetative cell
C. Germ cell
D. Body cell

Hint: gene of interest has to be introduced in such cells through which it can be passed on to next generations. To achieve so, the cells should be wisely selected.

Complete step by step answer:
Transgenic organisms can be produced by the process called genetic transformation. It is achieved by introducing an exogenous gene called a transgene into the organism’s genome. The organism thus exhibits the new character which can be transmitted to its offspring. It can only be achieved when the foreign gene is introduced into the nucleus of germ cells as they are the embryonic cell which develops into a gamete. It is the gamete which passes the introduced gene to the next generation. The integration of foreign DNA into somatic chromosomes can also induce expression that can persist through the lifetime of the organism, only drawback is that it cannot be inherited. Transgenic organisms are also called genetically modified organisms.

So, the correct answer is “Option C”.

Additional information-
advantages of developing transgenic organisms-
1. Disease resistance
2. Production of high yield
3. Rapid production
4. Antibiotic resistance
5. Induction of specific characters

Disadvantages-
1. Loss of biodiversity
2. High cost
3. May produce allergies
4. Might develop some undesired characters

Note:
For producing transgenic animals, the gene of interest should be introduced in to germ cells in order to make it possible to incorporate the gene in a manner that it passes on to the next generations. However, modern transformation techniques have various advancements. There are many processes to induce genetic transformation into organisms, different processes may be used for producing different organisms.