(a) ampR / ampicillin resistance genes, tetR/ tetracycline resistance gene.
They help in identifying and eliminating non -transformants/non recombinants and selectively permitting the growth of the transformants / recombinants.
(b) Simpler process / less cumbersome, in the presence of chromogenic substrate recombinants are colourless and non recombinants are blue in colour.
Detailed Answer:
(a) In cloning vector pBR322, ampicillin and tetracycline resistance genes serve as selectable markers. Selectable markers help in the identification and selection of transformed cells from non-transformed cells to distinguish the recombinant cells from the non-recombinant cells.
(b) The coding sequence of an enzyme β-galactosidase is preferred over antibiotic resistance genes because recombinants can be easily visualised and the process is comparatively simple and less cumbersome. When the foreign gene is inserted within the β-galactosidase gene, the enzyme p-galactosidase gets inactivated (insertional inactivation). Thus, when the bacteria are grown on a chromogenic substrate, non-recombinanats will produce blue-coloured colonies while the recombinants will produce colourless colonies.