X-Gal is also known 5-Bromo-4-chloro-3-indolyl-β-D-galactopyranoside and it is used to detect β-galactosidases. The lac Z gene encodes β-galactosidases which will cleave X-Gal to form an insoluble blue dimer. This is used in blue-white screening in E.coli, 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside
