Which method is used to introduce 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.

In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as biolistics or gene gun. And the last method uses ‘disarmed pathogen’ vectors, which when allowed to infect the cell, transfer the recombinant DNA into the host.