In a cloning experiment, one uses a vector that contains a lacZ gene near the unique restriction site. The white colonies would contain chromosomal DNA if the competent cells are grown on x-gal and IPTG.
The LacZ gene is in charge of making the beta-galactosidase enzyme. The mRNA fragment responsible for the manufacture of -galactosidase is encoded by the lacZ gene. Galactose and glucose are produced as a result of the enzyme's action on lactose.
While IPTG, or isopropyl beta-D-1-thiogalactopyranoside, causes the transcription of genes from the lac as well as tac operons in bacteria, X-Gal, or 5-Bromo-4-Chloro-3-Indolyl-beta-D-Galactoside, is a chromogenic substrate for the beta-galactosidase enzyme that produces a blue precipitate on hydrolysis.
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