G-banding is technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. The metaphase chromosomes are treated with trypsin (to partially digest the protein) and stained with Giemsa. Dark bands that take up the stain are strongly A,T rich (gene poor). The reverse of G-bands is obtained in R-banding. Banding can be used to identify chromosomal abnormalities, such as translocations, because there is a unique pattern of light and dark bands for each chromosome.