Question

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

• A. Recombinant colonies will produce blue colour in 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 colonies produce blue colour

Answer 1

Answer: (B)

• If a recombinant DNA is inserted within the coding sequence of $\beta$-galactosidase enzyme then non recombinant colonies will produce blue colour in presence of chromogenic substrate.
• In this a recombinant DNA is inserted within the coding sequence of an enzyme $\beta$-galactosidase.
• This results into inactivation of the 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.
• Presence of insert result into insertional inactivation of the $\beta$ -galactosidase and the colonies do not produce any colour these are identified as recombinant colonies.