In insertional inactivation, the coding sequence of which enzyme is d…

The correct answer is Option (1) → β-galactosidase

After DNA is put into bacteria, we need to find the colonies that carry recombinant DNA. One way uses the gene for the enzyme β-galactosidase. The foreign DNA is inserted inside the coding sequence of this gene. The gene is broken, and the enzyme is not made. This is called insertional inactivation. On a plate with a chromogenic (colour-forming) substrate, colonies without an insert make the enzyme and turn blue. Colonies with an insert cannot make the enzyme and stay colourless, so they are picked out as recombinants.

NCERT Extract:
Cloning Vectors – “… Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure because it requires simultaneous plating on two plates having different antibiotics. Therefore, alternative selectable markers have been developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. In this, a recombinant DNA is inserted within the coding sequence of an enzyme, β-galactosidase. This results into inactivation of the gene for synthesis of this enzyme, which is referred to as insertional inactivation. The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert.”