One method of detecting beta galactosidase is through its interaction with the substance X-gal. X-gal is a colorless compound which contains galactose linked to a modified indole molecule. When beta galactosidase interacts with X-gal, it breaks down, releasing the modified indole. This indole then dimerizes to produce an insoluble blue colored product. The reaction involving X-gal is easily carried out from single crystals of beta galactosidase. This process involved the use of a colorimetric assay. Another method is using fluorescein-di-beta-D-galactosidase (FDG) in flow cytometry for detecting gram-negative bacteria. It was shown that FDG could penetrate cells effectively and generate a fluorescent signal which directly correlated with the enzyme’s activity. This involved the use of a fluorometric assay. Another method involves the LacZ gene in E coli, which is commonly used as a reporter gene and a tracer in cell lineage studies. Researchers studying Drosophilafrequently use the detection of beta galactosidase to observe how cells and tissues develop within these insects.