Which technique is used to insert recombinant DNA into the nucleus of an animal cell?

Microinjection

The correct answer is Option (4) - Microinjection

Gene transfer involves the direct introduction of specific genes into the target organism's genome. This can be achieved using various techniques, such as microinjection, biolistics (gene gun method), or using disarmed pathogen vectors. These methods allow for precise insertion of desired genes without introducing unwanted genetic material.

In microinjection method, foreign DNA is indeed directly injected into the nucleus of an animal cell using microneedles. This is a technique used in genetic engineering to introduce foreign DNA into animal cells.