What is the first step in recombinant DNA technology?

The correct answer is Option (2) → Isolation of DNA

Recombinant DNA technology follows a set order: isolation of DNA, fragmentation of DNA by restriction endonucleases, isolation of the desired DNA fragment, ligation of the fragment into a vector, transfer of the recombinant DNA into the host, culturing of the host cells at a large scale and extraction of the desired product. Nothing can be cut or joined before pure DNA is in hand, so the process begins with isolation of DNA.

Option (1) Ligation of DNA fragment into a vector — Incorrect. Ligation into a vector comes only after the DNA has been isolated and cut, and the desired fragment has been separated.

Option (2) Isolation of DNA — Correct. Isolation of DNA is the first step. The cells are broken open and the DNA is purified, free from other macromolecules, so that restriction enzymes can cut it.

Option (3) Transferring recombinant DNA into the host — Incorrect. The recombinant DNA can be transferred into the host only after it has been made by ligation.

Option (4) Culturing host cells in a medium — Incorrect. Culturing the host cells in a medium at a large scale comes near the end, just before the desired product is extracted.

NCERT Extract:
Processes of Recombinant DNA Technology – “Recombinant DNA technology involves several steps in specific sequence such as isolation of DNA, fragmentation of DNA by restriction endonucleases, isolation of a desired DNA fragment, ligation of the DNA fragment into a vector, transferring the recombinant DNA into the host, culturing the host cells in a medium at large scale and extraction of the desired product.”