The blue and white selectable markers have been developed which differentiate recombinant colonies f

Question

The blue and white selectable markers have been developed which differentiate recombinant colonies from non-recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate.
 Given below are two statements about this method: 
Statement I: The blue coloured colonies have DNA insert in the plasmid and they are identified as recombinant colonies. 
Statement II: The colonies without blue colour have DNA insert in the plasmid and are identified as recombinant colonies. 
In the light of the above statements, choose the most appropriate answer from the options given below:

Professor PC Thomas Classes · Answer

(b) : The selection of recombinants and nonrecombinants can be done by insertional inactivation. The inactivation of a gene by insertion of a DNA sequence within it is known as insertional inactivation. In this, a recombinant DNA is inserted within the coding sequence of an enzyme, $\beta$-galactosidase. This result into inactivation of the gene for synthesis of this enzyme and the colonies do not produce any colour. These colonies are marked as recombinant colonies.