question_answer

Students while performing the experiment were given two different vectors for two different bacterial colonies that were cultured in a chromogenic substrate. They observed that the bacterial colonies with cloning vector A were colourless while those with cloning vector 'B' were blue in colour. Explain the phenomenon and the procedure behind the change in colour.

Answer:

Students were working to differentiate recombinants and non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. During this method, a recombinant DNA is inserted in the coding sequence of an enzyme \[\beta -\]galactosidase. This results in the inactivation of the enzyme (insertion inactivation). If the plasmid in the bacterium does not have an insert, it gives blue coloured (B) colonies. The presence of insert causes insertional inactivation and therefore, colourless (A) colonies are produced. These are marked as recombinant colonies.