Question: how to make x gal?
Answer: X-gal is 5-bromo-4-chloro-3-indolyl-β-D-galactoside. Make a 2% (w/v) stock solution by dissolving X-gal in dimethylformamide at a concentration of 20 mg/ml solution. Use a glass or polypropylene tube. Wrap the tube containing the solution in aluminum foil to prevent damage by light and store at -20°C.