Alien DNA can be introduced in the animal host cell by:

Using micro injection

The correct answer is Option (2) → Using micro injection

Microinjection: This technique involves directly injecting foreign (alien) DNA into the nucleus of an animal cell using a fine glass needle or micropipette. This method is precise and commonly used to introduce DNA into animal cells or embryos.

Gene gun: Another technique, suitable for plants, cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA. This method is known as biolistics or gene gun.

Treating with divalent ions: This method is typically used to make bacterial cells competent to take up DNA, not for animal cells.

Treating cells with cellulase: Cellulase breaks down cellulose in plant cell walls and is not relevant to animal cells, which lack cell walls.