Editing Karyotype (section)

=== Types of banding ===

[[Cytogenetics]] employs several techniques to visualize different aspects of chromosomes:<ref name="Gustashaw K.M 1991"/>
* [[G-banding]] is obtained with [[Giemsa stain]] following digestion of chromosomes with [[trypsin]]. It yields a series of lightly and darkly stained bands — the dark regions tend to be heterochromatic, late-replicating and AT rich. The light regions tend to be euchromatic, early-replicating and GC rich. This method will normally produce 300–400 bands in a normal, [[human genome]]. It is the most common chromosome banding method.<ref>{{cite book | last1=Maloy | first1=Stanley R. | last2=Hughes | first2=Kelly | title=Brenner's Encyclopedia of Genetics | publication-place=San Diego, CA | date=2013 | isbn=978-0-08-096156-9 | oclc=836404630 |publisher=Academic Press }}</ref>
* R-banding is the reverse of G-banding (the R stands for "reverse"). The dark regions are euchromatic (guanine-cytosine rich regions) and the bright regions are heterochromatic (thymine-adenine rich regions).
* C-banding: Giemsa binds to [[constitutive heterochromatin]], so it stains [[centromere]]s. The name is derived from centromeric or constitutive heterochromatin. The preparations undergo alkaline denaturation prior to staining leading to an almost complete depurination of the DNA. After washing the probe the remaining DNA is renatured again and stained with Giemsa solution consisting of methylene azure, methylene violet, methylene blue, and eosin. Heterochromatin binds a lot of the dye, while the rest of the chromosomes absorb only little of it. The C-bonding proved to be especially well-suited for the characterization of plant chromosomes.
* Q-banding is a [[fluorescent]] pattern obtained using [[quinacrine]] for staining. The pattern of bands is very similar to that seen in G-banding. They can be recognized by a yellow fluorescence of differing intensity. Most part of the stained DNA is heterochromatin. Quinacrin (atebrin) binds both regions rich in AT and in GC, but only the AT-quinacrin-complex fluoresces. Since regions rich in AT are more common in heterochromatin than in euchromatin, these regions are labelled preferentially. The different intensities of the single bands mirror the different contents of AT. Other fluorochromes like DAPI or Hoechst 33258 lead also to characteristic, reproducible patterns. Each of them produces its specific pattern. In other words: the properties of the bonds and the specificity of the fluorochromes are not exclusively based on their affinity to regions rich in AT. Rather, the distribution of AT and the association of AT with other molecules like histones, for example, influences the binding properties of the fluorochromes.
* T-banding: visualize [[telomere]]s.
* Silver staining: [[Silver nitrate]] stains the [[nucleolar organization region]]-associated protein.  This yields a dark region where the silver is deposited, denoting the activity of rRNA genes within the NOR.