A and B are two different cloning vectors in two different bacterial colonies cultured in chromogenic substrate. Bacterial colonies with cloning vector A were colourless, whereas those with B were blue coloured. Explain by giving reasons the cause of difference in colour that appeared.
On the basis of colour production in the presence of chromogenic substrate, the recombinants and non-recombinants can be differentiated. In this, a recombinant DNA is inserted within coding sequence of an enzyme (i-galactosidase, which results in inactivation of enzyme.
In plate A, the bacterial colonies having inserted plasmid, shows no colourisation. While in plate B, insertion of plasmid does not occur, therefore it shows blue colour.