(a) Ampicillin resistance gene (ampR) and tetracycline resistance gene (tetR) are the selectable markers in the cloning vector pBR322.[0.5+0.5]
Selectable marker, helps in identifying and eliminating non- transformants and selectively permitting the growth of the transformants. [1]
(b) β-galactosidase is preferred over antibiotic resistance genes because recombinants can be easily visualised and is less cumbersome.
In the presence of chromogenic substrate, recombinants are colourless and non-recombinants are blue in colour.[0.5+0.5]