Select the correct methods to introduce the recombinant DNA into the…

The correct answer is Option (1) → (A), (B) and (C) only

Recombinant DNA has to be introduced into a host cell, and the method depends on the host. Bacterial cells are first made competent and then given a brief heat shock at 42°C between two spells on ice. Animal and plant cells need other methods.

(A) Biolistics or gene gun for plant cells — Correct. Plant cells are bombarded with tiny gold or tungsten particles coated with DNA.

(B) Micro-injection for an animal cell — Correct. The recombinant DNA is injected directly into the nucleus of the animal cell.

(C) ‘Disarmed pathogen’ vectors — Correct. These vectors infect the cell and carry the recombinant DNA into the host.

(D) By heating the host cell at 100⁰ C and then cooling to 70⁰ C — Incorrect. The heat shock is a brief exposure to 42°C, with the cells kept on ice before and after. A temperature of 100°C would kill the cells.

NCERT Extract:
Cloning Vectors – “… Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 420C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA. This is not the only way to introduce alien DNA into host cells. In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell. 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.”