Chromosome Staining

Chromosome banding is based on differential staining properties of the chromosomes with special dyes. The most commonly used chromosomal banding technique is G-(Giemsa)-banding. If stained directly with Giemsa or Leishman, chromosomes display a uniform staining without any bands. However, banding appears if the air-dried chromosomal spreads on the slide are pretreated for approximately 1 minute with trypsin, an enzyme that digests proteins, and then stained with Giemsa or Leishman. Similar but less distinct bands are produced directly by staining with the fluorescent dyes quinacrine (Q-banding) or DAPI.

Dark bands in G-banding usually correspond to late-replicating regions; they tend to be enriched in AT-rich DNA and are relatively gene poor. Light bands typically corresponds to earlier-replicating regions, tend to be GC-rich DNA and more transcriptionally active.