Question

What would happen if a recombinant DNA is inserted within the coding sequence of an enzyme, $\beta$-galactosidase?

• A. This will result in the inactivation of the enzyme
• B. The presence of chromogenic substrate will give blue coloured colonies
• C. The recombinant colonies do not produce any colour
• D. Both (1) and (3) are correct

Answer 1

The correct option is D Both (1) and (3) are correct

Blue white screening or insertional inactivation is a kind of method of selection and screening of transformed cells. In this method, the recombinants are differentiated from non recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. The rDNA or recombinant DNA is inserted within the coding sequence of the enzyme galactosidase. This results in inactivation of the enzyme. In the presence of chromogenic substrate, blue coloured colonies are produced if the plasmid in the bacteria doesn't have the insert i.e. those are non recombinant. The presence of inserts in the bacteria (recombinant) result in the inactivation of galactosidase enzyme due to which colourless colonies are produced.

Hence, both options A and C are correct.

So, the correct answer is 'Both (1) and (3) are correct'.