The presence of chromogenic substrate gives blue coloured colonies,in presence of α-galactosidase. Presence of an insert (recombinant DNA) results into inactivation of the enzymer, colonies with inactivation of α-galactosidase do not produce any colour.
Detailed Answer :
The insertion of rDNA into the coding sequence of an enzyme alpha-galactosidase leads to the inactivation of the enzyme called insertional inactivation. The recombinants do not produce a blue coloured colonies in the presence of chromogenic substrate while the non-recombinants produce a blue colour.
