Which one of the following processes is used to identify the recombinant colonies?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Insertional inactivation
(1) Transformation — Incorrect. Transformation is the process by which a piece of DNA is taken up by a host bacterium. It brings the DNA in; it does not tell which colonies carry the insert.
(2) Gel electrophoresis — Incorrect. This separates DNA fragments by size in an agarose gel. It is used to check and purify DNA pieces, not to pick out colonies.
(3) Insertional inactivation — Correct. The foreign DNA is inserted inside the gene for the enzyme β-galactosidase, so the gene stops working. With a chromogenic substrate, colonies without an insert turn blue, while recombinant colonies give no colour. This is how recombinants are identified.
(4) Recombination — Incorrect. Recombination is the new combination of genes formed by crossing over during meiosis. It is not a selection method.
NCERT Extract:
Cloning Vectors – “… The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation of the β-galactosidase gene and the colonies do not produce any colour, these are identified as recombinant colonies.”