Question: how x gal and iptg works?
Answer: For screening the clones containing recombinant DNA, a chromogenic substrate known as X-gal is added to the agar plate. ... Isopropyl β-D-1-thiogalactopyranoside (IPTG) is used along with X-gal for blue-white screening. IPTG is a non-metabolizable analog of galactose that induces the expression of lacZ gene.