(a) a–Ampicillin resistance
d–Tetracycline.
(b) The insertion of rDNA into the coding sequence of an enzyme a-galactosidase leads to the inactivation of the enzyme called insertional inactivation. The recombinants do not produce a blue **** colonies in the presence of chromogenic substrate while the non-recombinants produce a blue colour. Thus, coding sequence of a-galactosidase is a better marker.
