Editing Karyotype (section)

== Diversity and evolution of karyotypes ==

Although the [[DNA replication|replication]] and [[transcription (genetics)|transcription]] of [[DNA]] is highly standardized in [[eukaryotes]], the same cannot be said for their karyotypes, which are highly variable. There is variation between species in chromosome number, and in detailed organization, despite their construction from the same [[Chromatin|macromolecules]]. This variation provides the basis for a range of studies in evolutionary [[cell biology|cytology]].

In some cases there is even significant variation within species. In a review, Godfrey and Masters conclude:

{{blockquote|In our view, it is unlikely that one process or the other can independently account for the wide range of karyotype structures that are observed ... But, used in conjunction with other phylogenetic data, karyotypic fissioning may help to explain dramatic differences in diploid numbers between closely related species, which were previously inexplicable.<ref>{{cite journal |vauthors=Godfrey LR, Masters JC |title=Kinetochore reproduction theory may explain rapid chromosome evolution |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=97 |issue=18 |pages=9821–3 |date=August 2000 |pmid=10963652 |pmc=34032 |bibcode=2000PNAS...97.9821G |doi=10.1073/pnas.97.18.9821|doi-access=free }}</ref>}}

Although much is known about karyotypes at the descriptive level, and it is clear that changes in karyotype organization has had effects on the evolutionary course of many species, it is quite unclear what the general significance might be.

{{blockquote|We have a very poor understanding of the causes of karyotype evolution, despite many careful investigations ... the general significance of karyotype evolution is obscure.|Maynard Smith<ref>Maynard Smith J. 1998. ''Evolutionary genetics''. 2nd ed, Oxford. p218-9</ref>}}

=== Changes during development ===

Instead of the usual gene repression, some organisms go in for large-scale elimination of [[heterochromatin]], or other kinds of visible adjustment to the karyotype.
* Chromosome elimination. In some species, as in many [[Sciaridae|sciarid flies]], entire chromosomes are eliminated during development.<ref>{{cite journal |vauthors=Goday C, Esteban MR |title=Chromosome elimination in sciarid flies |journal=BioEssays |volume=23 |issue=3 |pages=242–50 |date=March 2001 |pmid=11223881 |doi=10.1002/1521-1878(200103)23:3<242::AID-BIES1034>3.0.CO;2-P |s2cid=43718856 }}</ref>
* Chromatin diminution (founding father: [[Theodor Boveri]]). In this process, found in some [[copepods]] and [[roundworms]] such as ''[[Ascaris suum]]'', portions of the chromosomes are cast away in particular cells. This process is a carefully organised genome rearrangement where new telomeres are constructed and certain heterochromatin regions are lost.<ref>{{cite journal |vauthors=Müller F, Bernard V, Tobler H |title=Chromatin diminution in nematodes |journal=BioEssays |volume=18 |issue=2 |pages=133–8 |date=February 1996 |pmid=8851046 |doi=10.1002/bies.950180209 |s2cid=24583845 }}</ref><ref>{{cite journal |vauthors=Wyngaard GA, Gregory TR |title=Temporal control of DNA replication and the adaptive value of chromatin diminution in copepods |journal=J. Exp. Zool. |volume=291 |issue=4 |pages=310–6 |date=December 2001 |pmid=11754011 |doi=10.1002/jez.1131|bibcode=2001JEZ...291..310W }}</ref> In ''A. suum'', all the somatic cell precursors undergo chromatin diminution.<ref>Gilbert S.F. 2006. ''Developmental biology''. Sinauer Associates, Stamford CT. 8th ed, Chapter 9</ref>
* [[X-inactivation]]. The inactivation of one X chromosome takes place during the early development of mammals (see [[Barr body]] and [[dosage compensation]]). In [[placental mammals]], the inactivation is random as between the two Xs; thus the mammalian female is a mosaic in respect of her X chromosomes. In [[marsupials]] it is always the paternal X which is inactivated. In human females some 15% of somatic cells escape inactivation,<ref>{{harvnb|King|Stansfield|Mulligan|2006}}</ref> and the number of genes affected on the inactivated X chromosome varies between cells: in [[fibroblast]] cells up about 25% of genes on the Barr body escape inactivation.<ref>{{cite journal |vauthors=Carrel L, Willard H | year = 2005 | title = X-inactivation profile reveals extensive variability in X-linked gene expression in females | journal = Nature | volume = 434 | issue = 7031| pages = 400–404 | doi = 10.1038/nature03479 | pmid = 15772666 | bibcode = 2005Natur.434..400C | s2cid = 4358447 }}</ref>

=== Number of chromosomes in a set ===

A spectacular example of variability between closely related species is the [[muntjac]], which was investigated by [[Kurt Benirschke]] and [[Doris Wurster]]. The diploid number of the Chinese muntjac, ''[[Muntiacus reevesi]]'', was found to be 46, all [[telocentric]]. When they looked at the karyotype of the closely related Indian muntjac, ''[[Muntiacus muntjak]]'', they were astonished to find it had female = 6, male = 7 chromosomes.<ref>{{cite journal |vauthors=Wurster DH, Benirschke K |title=Indian muntjac, ''Muntiacus muntjak'': a deer with a low diploid chromosome number |journal=Science |volume=168 |issue=3937 |pages=1364–6 |date=June 1970 |pmid=5444269 |doi=10.1126/science.168.3937.1364|bibcode = 1970Sci...168.1364W |s2cid=45371297 }}</ref>

{{blockquote|They simply could not believe what they saw ... They kept quiet for two or three years because they thought something was wrong with their tissue culture ... But when they obtained a couple more specimens they confirmed [their findings].|Hsu p. 73-4<ref name="Hsu"/>}}

The number of chromosomes in the karyotype between (relatively) unrelated species is hugely variable. The low record is held by the [[nematode]] ''[[Parascaris univalens]]'', where the [[haploid]] n = 1; and an ant: ''[[Myrmecia pilosula]]''.<ref>{{cite journal|author1=Crosland M.W.J.  |author2=Crozier, R.H.|year=1986|title=''Myrmecia pilosula'', an ant with only one pair of chromosomes|journal=Science|volume=231|pages=1278|doi=10.1126/science.231.4743.1278|pmid=17839565|issue=4743|bibcode=1986Sci...231.1278C|s2cid=25465053}}</ref> The high record would be somewhere amongst the [[fern]]s, with the adder's tongue fern ''[[Ophioglossum]]'' ahead with an average of 1262 chromosomes.<ref>{{cite journal |author=Khandelwal S. |title=Chromosome evolution in the genus Ophioglossum L |journal=Botanical Journal of the Linnean Society |volume=102 |pages=205–217 |year=1990 |doi=10.1111/j.1095-8339.1990.tb01876.x |issue=3 }}</ref> Top score for animals might be the [[shortnose sturgeon]] ''[[Acipenser brevirostrum]]'' at 372 chromosomes.<ref name=Kim2005>{{cite journal |first=D.S. |last=Kim |author2=Nam, Y.K. |author3=Noh, J.K. |author4=Park, C.H. |author5=Chapman, F.A. | year = 2005 | title = Karyotype of North American shortnose sturgeon ''Acipenser brevirostrum'' with the highest chromosome number in the Acipenseriformes | journal = Ichthyological Research | volume = 52 | issue = 1 | pages = 94–97 | doi = 10.1007/s10228-004-0257-z|bibcode=2005IchtR..52...94K |s2cid=20126376 }}</ref> The existence of supernumerary or [[B chromosomes]] means that chromosome number can vary even within one interbreeding population; and [[aneuploid]]s are another example, though in this case they would not be regarded as normal members of the population.

===Fundamental number===

The fundamental number, ''FN'', of a karyotype is the number of visible major chromosomal arms per set of chromosomes.<ref name = "Matthey">{{Cite journal
  | last = Matthey | first = R. 
  | title = L'evolution de la formule chromosomiale chez les vertébrés
  | journal = Experientia (Basel)
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}}</ref><ref name = "Oliveira">{{Cite journal
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  | title = Karyotype characterization and ZZ/ZW sex chromosome heteromorphism in two species of the catfish genus ''Ancistrus'' Kner, 1854 (Siluriformes: Loricariidae) from the Amazon basin
  | journal = [[Neotropical Ichthyology]] | volume = 5 | issue = 3 | pages = 301–6
  | date = July–September 2007
  | doi = 10.1590/S1679-62252007000300010
  | doi-access = free
}}</ref> Thus, FN ≤ 2 × 2n, the difference depending on the number of chromosomes considered single-armed ([[Centromere#Acrocentric|acrocentric]] or [[Centromere#Telocentric|telocentric]]) present. Humans have FN = 82,<ref name = "Pellicciari">{{Cite journal
  | last1 = Pellicciari | first1 = C.
  | last2=Formenti |first2=D. |last3=Redi |first3=C. A. |last4=Manfredi |first4=M. G. |author5=Romanini
  | title = DNA content variability in primates
  | journal = [[Journal of Human Evolution]] | volume = 11 | issue = 2 | pages = 131–141
  | date = February 1982
  | doi = 10.1016/S0047-2484(82)80045-6
| bibcode = 1982JHumE..11..131P
 }}</ref> due to the presence of five acrocentric chromosome pairs: [[Chromosome 13 (human)|13]], [[Chromosome 14 (human)|14]], [[Chromosome 15 (human)|15]], [[Chromosome 21 (human)|21]], and [[Chromosome 22 (human)|22]] (the human [[Y chromosome]] is also acrocentric). The fundamental autosomal number or autosomal fundamental number, ''FNa''<ref name = "Souza">{{cite journal
  | last1 = Souza | first1 = A. L. G.
  | last2=de O. Corrêa |first2=M. M. |last3=de Aguilar |first3=C. T. |last4=Pessôa |first4=L. M.
  | title = A new karyotype of ''Wiedomys pyrrhorhinus'' (Rodentia: Sigmodontinae) from Chapada Diamantina, northeastern Brazil
  | journal = Zoologia | volume = 28 | issue = 1 | pages = 92–96
  | date = February 2011
  | url = http://www.scielo.br/pdf/zool/v28n1/v28n1a13.pdf | doi = 10.1590/S1984-46702011000100013
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}}</ref> or ''AN'',<ref name = "Weksler">{{cite journal
  | last1        = Weksler
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  | title        = Taxonomy of pygmy rice rats genus ''Oligoryzomys'' Bangs, 1900 (Rodentia, Sigmodontinae) of the Brazilian Cerrado, with the description of two new species
  | journal      = Arquivos do Museu Nacional, Rio de Janeiro
  | volume       = 63
  | issue        = 1
  | pages        = 113–130
  | date         = 2005-01-03
  | url          = http://www.publicacao.museunacional.ufrj.br/Arquivos/Arq632005/Arq631/10Arq631.pdf
  | issn         = 0365-4508
  | access-date  = 22 April 2012
  | archive-url  = https://web.archive.org/web/20120326085915/http://www.publicacao.museunacional.ufrj.br/Arquivos/Arq632005/Arq631/10Arq631.pdf
  | archive-date = 26 March 2012
  | url-status   = dead
}}</ref> of a karyotype is the number of visible major chromosomal arms per set of [[autosome]]s (non-[[allosome|sex-linked chromosomes]]).

=== Ploidy ===
{{for|the investigation of ancient karyotype duplications|Paleopolyploidy}}
[[Ploidy]] is the number of complete sets of chromosomes in a cell.
* [[Polyploidy]], where there are more than two sets of homologous chromosomes in the cells, occurs mainly in plants. It has been of major significance in plant evolution according to [[G. Ledyard Stebbins|Stebbins]].<ref>{{cite journal |first=G. L. |last=Stebbins |title=The significance of polyploidy in plant evolution |journal=The American Naturalist |volume=74 |pages=54–66 |year=1940 |doi=10.1086/280872 |issue=750 |bibcode=1940ANat...74...54S |s2cid=86709379 }}</ref><ref>{{harvnb|Stebbins|1950}}</ref><ref>{{cite journal |last=Comai |first=L. |title=The advantages and disadvantages of being polyploid |journal=Nature Reviews Genetics |volume=6 |issue=11 |pages=836–46 |date=November 2005 |pmid=16304599 |doi=10.1038/nrg1711 |s2cid=3329282 }}</ref><ref>{{cite journal |vauthors=Adams KL, Wendel JF |title=Polyploidy and genome evolution in plants |journal=Current Opinion in Plant Biology |volume=8 |issue=2 |pages=135–141 |date=April 2005 |pmid=15752992 |doi=10.1016/j.pbi.2005.01.001 |bibcode=2005COPB....8..135A }}</ref> The proportion of flowering plants which are polyploid was estimated by Stebbins to be 30–35%, but in grasses the average is much higher, about 70%.<ref>{{harvnb|Stebbins|1971}}</ref> Polyploidy in lower plants ([[fern]]s, [[horsetails]] and [[psilotales]]) is also common, and some species of ferns have reached levels of polyploidy far in excess of the highest levels known in flowering plants. Polyploidy in animals is much less common, but it has been significant in some groups.<ref>{{cite book |last1=Gregory |first1=T. R. |last2=Mable |first2=B. K. |chapter=Ch. 8: Polyploidy in animals |editor-first=T. Ryan |editor-last=Gregory |title=The Evolution of the Genome |chapter-url=https://books.google.com/books?id=8HtPZP9VSiMC&pg=PA427 |year=2011 |publisher=Academic Press |isbn=978-0-08-047052-8 |pages=427–517 }}</ref><p>Polyploid series in related species which consist entirely of multiples of a single basic number are known as [[euploid]].</p>
* [[Haplo-diploid sex-determination system|Haplo-diploidy]], where one sex is [[diploid]], and the other [[haploid]]. It is a common arrangement in the [[Hymenoptera]], and in some other groups.
* [[Endopolyploidy]] occurs when in adult [[Cellular differentiation|differentiated]] tissues the cells have ceased to divide by [[mitosis]], but the [[Cell nucleus|nuclei]] contain more than the original [[somatic cell|somatic]] number of [[chromosomes]].<ref>{{cite book |last=White |first=M. J. D. |title=The chromosomes |url=https://archive.org/details/chromosomes01whit |url-access=registration |publisher=Chapman & Hall |location=London |year=1973 |edition=6th |page=[https://archive.org/details/chromosomes01whit/page/n58 45] }}</ref> In the ''endocycle'' ([[endomitosis]] or [[endoreduplication]]) chromosomes in a 'resting' nucleus undergo [[reduplication]], the daughter chromosomes separating from each other inside an ''intact'' [[nuclear membrane]].<ref name=Lilly>{{cite journal |last1=Lilly |first1=M. A. |last2=Duronio |first2=R. J. | title = New insights into cell cycle control from the ''Drosophila'' endocycle | journal = Oncogene | volume = 24 | issue = 17 | pages = 2765–75 | year = 2005 | pmid = 15838513 | doi = 10.1038/sj.onc.1208610| doi-access = free }}</ref><p>In many instances, endopolyploid nuclei contain tens of thousands of chromosomes (which cannot be exactly counted). The cells do not always contain exact multiples (powers of two), which is why the simple definition 'an increase in the number of chromosome sets caused by replication without cell division' is not quite accurate.</p><p>This process (especially studied in insects and some higher plants such as maize) may be a developmental strategy for increasing the productivity of tissues which are highly active in biosynthesis.<ref>{{cite journal |vauthors=Edgar BA, Orr-Weaver TL |title=Endoreplication cell cycles: more for less |journal=Cell |volume=105 |issue=3 |pages=297–306 |date=May 2001 |pmid=11348589 |doi=10.1016/S0092-8674(01)00334-8|s2cid=14368177 |doi-access=free }}</ref></p><p>The phenomenon occurs sporadically throughout the [[eukaryote]] kingdom from [[protozoa]] to humans; it is diverse and complex, and serves [[differentiation (cellular)|differentiation]] and [[morphogenesis]] in many ways.<ref>{{cite book |last=Nagl |first=W. |year=1978 |title=Endopolyploidy and polyteny in differentiation and evolution: towards an understanding of quantitative and qualitative variation of nuclear DNA in ontogeny and phylogeny |publisher=Elsevier |location=New York}}</ref></p>

=== Aneuploidy ===

[[Aneuploidy]] is the condition in which the chromosome number in the cells is not the typical number for the species. This would give rise to a [[chromosome abnormality]] such as an extra chromosome or one or more chromosomes lost. Abnormalities in chromosome number usually cause a defect in development. [[Down syndrome]] and [[Turner syndrome]] are examples of this.

Aneuploidy may also occur within a group of closely related species. Classic examples in plants are the genus ''[[Crepis]]'', where the gametic (= haploid) numbers form the series x = 3, 4, 5, 6, and 7; and ''[[Crocus]]'', where every number from x = 3 to x = 15 is represented by at least one species. Evidence of various kinds shows that trends of evolution have gone in different directions in different groups.<ref>Stebbins, G. Ledley, Jr. 1972. ''Chromosomal evolution in higher plants''. Nelson, London. p18</ref> In primates, the [[great apes]] have 24x2 chromosomes whereas humans have 23x2. [[Human chromosome 2]] was formed by a merger of ancestral chromosomes, reducing the number.<ref>{{cite journal |vauthors=IJdo JW, Baldini A, Ward DC, Reeders ST, Wells RA |title=Origin of human chromosome 2: an ancestral telomere-telomere fusion |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=88 |issue=20 |pages=9051–5 |date=October 1991 |pmid=1924367 |pmc=52649 |bibcode=1991PNAS...88.9051I |doi=10.1073/pnas.88.20.9051|doi-access=free }}</ref>

=== Chromosomal polymorphism ===

Some species are [[Polymorphism (biology)|polymorphic]] for different chromosome structural forms.<ref>{{cite book |author1=Rieger, R. |author2=Michaelis, A. |author3=Green, M.M. |year=1968  |title=A glossary of genetics and cytogenetics: Classical and molecular |url=https://archive.org/details/glossaryofgeneti00rieg |url-access=registration |publisher=Springer-Verlag |location=New York |isbn=9780387076683 }}</ref> The structural variation may be associated with different numbers of chromosomes in different individuals, which occurs in the ladybird beetle ''[[Chilocorus stigma]]'', some [[mantids]] of the genus ''[[Ameles]]'',<ref>{{cite journal |last1=Gustavsson |first1=Ingemar |date=3 March 1969 |title= Cytogenetics, distribution and phenotypic effects of a translocation in Swedish cattle.|url= |journal=Hereditas |volume=63 |issue= 1–2|pages=68–169 |doi= 10.1111/j.1601-5223.1969.tb02259.x|pmid=5399228 |access-date=}}</ref> the European shrew ''[[Sorex araneus]]''.<ref>{{Cite journal|last=Searle|first=J. B.|date=1984-06-01|title=Three New Karyotypic Races of the Common Shrew Sorex Araneus (Mammalia: Insectivora) and a Phylogeny|journal=Systematic Biology|volume=33|issue=2|pages=184–194|doi=10.1093/sysbio/33.2.184|issn=1063-5157}}</ref> There is some evidence from the case of the [[mollusc]] ''[[Thais lapillus]]'' (the [[dog whelk]]) on the [[Brittany]] coast, that the two chromosome morphs are [[Adaptation|adapted]] to different habitats.<ref>{{harvnb|White|1973|p=169}}</ref>

=== Species trees ===

The detailed study of chromosome banding in insects with [[polytene chromosome]]s can reveal relationships between closely related species: the classic example is the study of chromosome banding in [[Hawaiian Drosophilidae|Hawaiian drosophilids]] by [[Hampton L. Carson (biologist)|Hampton L. Carson]].

In about {{convert|6500|sqmi|km2|abbr=on}}, the [[Hawaiian Islands]] have the most diverse collection of drosophilid flies in the world, living from [[Hawaiian tropical rainforests|rainforests]] to [[Hawaiian tropical high shrublands|subalpine meadows]]. These roughly 800 Hawaiian drosophilid species are usually assigned to two genera, ''[[Drosophila]]'' and ''[[Drosophila|Scaptomyza]]'', in the family [[Drosophilidae]].

The polytene banding of the 'picture wing' group, the best-studied group of Hawaiian drosophilids, enabled Carson to work out the evolutionary tree long before genome analysis was practicable. In a sense, gene arrangements are visible in the banding patterns of each chromosome. Chromosome rearrangements, especially [[Chromosome inversions|inversions]], make it possible to see which species are closely related.

The results are clear. The inversions, when plotted in tree form (and independent of all other information), show a clear "flow" of species from older to newer islands. There are also cases of colonization back to older islands, and skipping of islands, but these are much less frequent. Using [[radiometric dating|K-Ar]] dating, the present islands date from 0.4 million years ago (mya) ([[Mauna Kea]]) to 10mya ([[Necker Island (Northwestern Hawaiian Islands)|Necker]]). The oldest member of the Hawaiian archipelago still above the sea is [[Kure Atoll]], which can be dated to 30 mya. The archipelago itself (produced by the [[Pacific Plate]] moving over a [[Hot spot (geology)|hot spot]]) has existed for far longer, at least into the [[Cretaceous]]. Previous islands now beneath the sea ([[guyot]]s) form the [[Hawaiian-Emperor seamount chain|Emperor Seamount Chain]].<ref>{{cite book |author1=Clague, D.A. |author2=Dalrymple, G.B. |chapter=The Hawaiian-Emperor volcanic chain, Part I. Geologic evolution |editor1=Decker, R.W. |editor2=Wright, T.L. |editor3=Stauffer, P.H. |title=Volcanism in Hawaii |id=U.S. Geological Survey Professional Paper 1350 |year=1987 |pages=5–54 |chapter-url=http://pubs.usgs.gov/pp/1987/1350/pp1350_vol1.pdf |volume=1 |archive-date=10 October 2012 |access-date=28 May 2013 |archive-url=https://web.archive.org/web/20121010062038/http://pubs.usgs.gov/pp/1987/1350/pp1350_vol1.pdf |url-status=dead }}</ref>

All of the native ''Drosophila'' and ''Scaptomyza'' species in Hawai{{okina}}i have apparently descended from a single ancestral species that colonized the islands, probably 20 million years ago. The subsequent [[adaptive radiation]] was spurred by a lack of [[Competition (biology)|competition]] and a wide variety of [[Vacant niche|niches]]. Although it would be possible for a single [[gravid]] female to colonise an island, it is more likely to have been a group from the same species.<ref>{{cite journal |author=Carson HL |title=Chromosome tracers of the origin of species |journal=Science |volume=168 |issue=3938 |pages=1414–8 |date=June 1970 |pmid=5445927 |bibcode=1970Sci...168.1414C |doi=10.1126/science.168.3938.1414}}</ref><ref>{{cite journal |author=Carson HL |title=Chromosomal sequences and interisland colonizations in Hawaiian ''Drosophila'' |journal=Genetics |volume=103 |issue=3 |pages=465–82 |date=March 1983 |doi=10.1093/genetics/103.3.465 |pmid=17246115 |pmc=1202034 |url=http://www.genetics.org/cgi/pmidlookup?view=long&pmid=17246115}}</ref><ref>{{cite book |author=Carson H.L. |chapter=Inversions in Hawaiian ''Drosophila'' |editor1=Krimbas, C.B. |editor2=Powell, J.R. |title=Drosophila inversion polymorphism |publisher=CRC Press |location=Boca Raton FL |year=1992 |isbn=978-0849365478 |pages=407–439 }}</ref><ref>{{cite book |author1=Kaneshiro, K.Y. |author2=Gillespie, R.G. |author3=Carson, H.L. |chapter=Chromosomes and male genitalia of Hawaiian Drosophila: tools for interpreting phylogeny and geography |editor1=Wagner, W.L. |editor2=Funk, E. |title=Hawaiian biogeography: evolution on a hot spot archipelago |chapter-url=https://archive.org/details/hawaiianbiogeogr00wagn |publisher=Smithsonian Institution Press |location=Washington DC |year=1995 |pages=[https://archive.org/details/hawaiianbiogeogr00wagn/page/57 57–71] }}</ref>

There are other animals and plants on the Hawaiian archipelago which have undergone similar, if less spectacular, adaptive radiations.<ref>{{cite book |author=Craddock E.M. |chapter=Speciation Processes in the Adaptive Radiation of Hawaiian Plants and Animals |title=Evolutionary Biology |editor1-first=Max K. |editor1-last=Hecht |editor2-first=Ross J. |editor2-last=MacIntyre |editor3-first=Michael T. |editor3-last=Clegg |volume=31 |pages=1–43 |year=2000 |doi=10.1007/978-1-4615-4185-1_1 |isbn=978-1-4613-6877-9 }}</ref><ref>{{cite book |first=Alan C. |last=Ziegler |title=Hawaiian natural history, ecology, and evolution |url=https://books.google.com/books?id=l56J_8teG58C |year=2002 |publisher=University of Hawaii Press |isbn=978-0-8248-2190-6}}</ref>

=== Chromosome banding ===

Chromosomes display a banded pattern when treated with some stains. Bands are alternating light and dark stripes that appear along the lengths of chromosomes. Unique banding patterns are used to identify chromosomes and to diagnose chromosomal aberrations, including chromosome breakage, loss, duplication, translocation or inverted segments. A range of different chromosome treatments produce a range of banding patterns: G-bands, R-bands, C-bands, Q-bands, T-bands and NOR-bands.