Question

If a recombinant DNA is inserted within the coding sequence of β-galactosidase enzyme, then

• A. recombinant colonies will give blue colour in the presence of chromogenic substrate
• B. non–recombinant colonies, will produce blue colour in presence of chromogenic substrate
• C. non–recombinant colonies will not produce colour due to insertional inactivation
• D. both recombinant and non-recombinant colours produce blue colour

Answer 1

The correct option is B non–recombinant colonies, will produce blue colour in presence of chromogenic substrate

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 does not 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.
So, if a recombinant DNA is inserted within the coding sequence of $\beta$ – galactosidase enzyme than non–recombinant colonies will produce blue colour in presence of chromogenic substrate.