Used in conjunction with IPTG to identify bacterial colonies that contain recombinant plasmids by blue/white selection. X-Gal forms an intense blue precipitate in the presence of β-Galactosidase. Insoluble. Reaction Condition: Stocks: X-Gal 20 mg/ml in DMF; IPTG 20 mg/ml in water. Mix 4:1 (X-Gal/IPTG) for spreading onto agar plates prior to plating transformed bacteria.