The gene of lac operon that can be used as selectable marker in genetic engineering to identify the recombinant transfromants from non-recombinant transformants is

Gene for β-galactosidase i.e. gene ‘z’ of lac operon is used selectable marker as this enzyme converts the colorless X-gal substrate into blue colored products, it is used as selectable marker to identify the colorless recombinant transformant colonies from blue colored non-recombinant transformant colonies of bacteria.