The
metaphase chromosomes are treated with
trypsin (to partially digest the chromosome) and
stained with
Giemsa stain.
Heterochromatic regions, which tend to be rich with
guanine and
cytosine (GC-rich) DNA and relatively gene-poor, stain lighter in G-banding. In contrast, less condensed chromatin (
Euchromatin)—which tends to be rich with
adenine and
thymine (
AT-rich) and more
transcriptionally active—incorporates less
Giemsa stain, and these regions appear as dark bands in G-banding. The pattern of bands are numbered on each arm of the
chromosome from the
centromere to the
telomere. This numbering system allows any
band on the
chromosome to be identified and described precisely. The reverse of G‑bands is obtained in
R‑banding. Staining with Giemsa confers a purple color to chromosomes, but micrographs are often converted to
grayscale to facilitate data presentation and make comparisons of results from different laboratories. The less condensed the chromosomes are, the more bands appear when G-banding. This means that the different chromosomes are more distinct in
prophase than they are in metaphase. File:Human Chromosomes (crop).jpg|Micrograph of human male chromosomes using Giemsa staining for G banding. File:NHGRI human male karyotype.png|Micrograph of human male chromosomes using Giemsa stain, followed by sorting and
grayscaling. ==Advantage==