For selection of recombinants,insertional inactivation of antibiotic marker has been superceded by insertional inactivation of a marker gene coding for a chromogenic substrate. Give reasons.

(D) Selection of recombinants due to inactivation of antibiotics is a laborious process as it requires: $(i)$ a vector with two antibiotic (ampicillin and tetracycline) resistance markers.
$(ii)$ preparation of two kinds of media plates,each containing one antibiotic.
Transformed cells are first plated on the antibiotic plate that has not been insertionally inactivated (e.g.,ampicillin) and incubated overnight for the growth of transformants. For the selection of recombinants,these transformants are replica-plated on the second antibiotic (tetracycline) plate,which has been inactivated due to the insertion of the foreign gene. Non-recombinants grow on both plates,while recombinants grow only on the ampicillin plate.
This entire exercise is laborious and time-consuming,requiring two overnight incubations. However,by using a marker gene that produces color in the presence of a chromogenic substrate (e.g.,$\beta$-galactosidase),we can distinguish between recombinants and non-recombinants on a single medium plate containing one antibiotic and the chromogenic compound after a single overnight incubation. Thus,using a chromogenic marker is more efficient.