Question

If a person obtains transformants by inserting a recombinant DNA within the coding sequence of enzyme -galactosidase, he will separate out recombinants from non-recombinants by which of the following observations?

• A. Non-recombinant colonies do not produce any colour whereas recombinants give blue coloured colonies
• B. Recombinant colonies do not produce any colour whereas non-recombinants give blue coloured colonies
• C. Recombinants and non-recombinants both produce blue coloured colonies
• D. No colonies are formed due to insertional inactivation

Answer 1

The correct option is B Recombinant colonies do not produce any colour whereas non-recombinants give blue coloured colonies

Alternative selectable markers have been developed which differentiate recombinants from the 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, ( -galactosidase. This results into inactivation of the enzyme, which is referred i to as insertional inactivation. The presence of a chromogenic j 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 -galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.