(a)A recombinant vector with a gene of interest inserted within the gene of $\alpha $-galactosidase enzyme, is introduced into a bacterium.Explain the method that would help in selection of recombinant colonies from non-recombinant ones

(a)A recombinant vector with a gene of interest inserted within the gene of $\alpha $-galactosidase enzyme, is introduced into a bacterium.Explain the method that would help in selection of recombinant colonies from non-recombinant ones.
(b)Why is this method of selection reffered to as ‘‘insertional inactivation’’?

(a) Bacteria is grown in a medium with chromogenic substrate, colonies formed show blue colour-no recombinants, no blue colour- presence of recombinants.
(b)Gene for the enzyme is inactivated by insertion.