G banding

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G-banding: Micrograph of a karyogram of human male using Giemsa staining.
G-banding: Schematic karyogram of human male.

G-banding, G banding or Giemsa banding is a technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. It is the most common chromosome banding method.[1] It is useful for identifying genetic diseases through the photographic representation of the entire chromosome complement.[2] 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 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. 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.[3] 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.[2]

It is difficult to identify and group chromosomes based on simple staining because the uniform colour of the structures makes it difficult to differentiate between the different chromosomes. Therefore, techniques like G‑banding were developed that made "bands" appear on the chromosomes. These bands were the same in appearance on the homologous chromosomes, thus, identification became easier and more accurate. 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.[4]

Other types of cytogenic banding are listed below:

Banding type Staining method
C-banding Constitutive heterochromatin
G-banding Giemsa stain
Q-banding Quinacrine
R-banding Reverse Giemsa staining
T-banding Telomeric

See also[edit]


  1. ^ Maloy, Stanley R.; Hughes, Kelly (2013). Brenner's encyclopedia of genetics. San Diego, CA. ISBN 978-0-08-096156-9. OCLC 836404630.
  2. ^ a b Speicher, Michael R. and Nigel P. Carter. "The New Cytogenetics: Blurring the Boundaries with Molecular Biology." Nature Reviews Genetics, Vol 6. Oct 2005.
  3. ^ Nussbaum, Robert; McInnes, Roderick; Willard, Huntington (2015). Thompson & Thompson, Genetics in Medicine (Eighth ed.). Canada: Elsevier Inc. p. 58. ISBN 978-1-4377-0696-3.
  4. ^ Nussbaum, McInnes, Willard (21 May 2015). Genetics in Medicine. Elsevier. pp. 57–73. ISBN 978-1-4377-0696-3.{{cite book}}: CS1 maint: multiple names: authors list (link)