G banding

Heterochromatic regions, which tend to be rich with adenine and thymine (AT-rich) DNA and relatively gene-poor, stain more darkly in G-banding.

In contrast, less condensed chromatin (Euchromatin)—which tends to be rich with guanine and cytosine (GC-rich) and more transcriptionally active—incorporates less Giemsa stain, and these regions appear as light bands in G-banding.

[3] The pattern of bands are numbered on each arm of the chromosome from the centromere to the telomere.

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.

These bands were the same in appearance on the homologous chromosomes, thus, identification became easier and more accurate.

Schematic karyogram of a human as seen on G banding, with annotated bands and sub-bands . It is a graphical representation of the idealized human diploid karyotype. Each row is vertically aligned at centromere level. It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes , as well as the mitochondrial genome (at bottom left).
Further information: Karyotype