Editing Karyotype (section)

== History of karyotype studies ==

Chromosomes were first observed in plant cells by [[Carl Wilhelm von Nägeli]] in 1842. Their behavior in animal ([[salamander]]) cells was described by [[Walther Flemming]], the discoverer of [[mitosis]], in 1882. The name was coined by another German anatomist, [[Heinrich Wilhelm Gottfried von Waldeyer-Hartz|Heinrich von Waldeyer]] in 1888. It is [[Neo-Latin]] from [[Ancient Greek]] κάρυον ''karyon'', "kernel", "seed", or "nucleus", and τύπος ''typos'', "general form")

The next stage took place after the development of genetics in the early 20th century, when it was appreciated that chromosomes (that can be observed by karyotype) were the carrier of genes. The term karyotype as defined by the [[phenotypic]] appearance of the [[Somatic (biology)|somatic]] chromosomes, in contrast to their [[gene|genic]] contents was introduced by [[Grigory Levitsky]] who worked with Lev Delaunay, [[Sergei Navashin]], and [[Nikolai Vavilov]].<ref>{{Cite journal |last1=Zelenin |first1=A. V. |last2=Rodionov |first2=A. V. |last3=Bolsheva |first3=N. L. |last4=Badaeva |first4=E. D. |last5=Muravenko |first5=O. V. |date=2016 |title=Genome: Origins and evolution of the term |url=http://link.springer.com/10.1134/S0026893316040178 |journal=Molecular Biology |language=en |volume=50 |issue=4 |pages=542–550 |doi=10.1134/S0026893316040178 |pmid=27668601 |s2cid=9373640 |issn=0026-8933}}</ref><ref>{{Cite journal |last1=Vermeesch |first1=Joris Robert |last2=Rauch |first2=Anita |date=2006 |title=Reply to Hochstenbach et al |journal=European Journal of Human Genetics |language=en |volume=14 |issue=10 |pages=1063–1064 |doi=10.1038/sj.ejhg.5201663 |pmid=16736034 |s2cid=46363277 |issn=1018-4813|doi-access=free }}</ref><ref>Delaunay L. N.  ''Comparative karyological study of species Muscari Mill. and Bellevalia Lapeyr''. Bulletin of the Tiflis Botanical Garden. 1922, v. 2, n. 1, p. 1-32[in Russian]</ref><ref>{{cite journal |last1=Battaglia |first1=Emilio |title=Nucleosome and nucleotype: a terminological criticism |journal=Caryologia |volume=47 |issue=3–4 |pages=193–197 |year=1994 |doi=10.1080/00087114.1994.10797297}}</ref> The subsequent history of the concept can be followed in the works of [[C. D. Darlington]]<ref>Darlington C.D. 1939. ''Evolution of genetic systems''. Cambridge University Press. 2nd ed, revised and enlarged, 1958. Oliver & Boyd, Edinburgh.</ref> and [[Michael JD White]].<ref name="White2"/><ref name="White1">White M.J.D. 1973. ''Animal cytology and evolution''. 3rd ed, Cambridge University Press.</ref>

Investigation into the human karyotype took many years to settle the most basic question: how many chromosomes does a normal [[diploid]] human cell contain?<ref>{{cite journal |first1=Kottler |last1=MJ |title=From 48 to 46: cytological technique, preconception, and the counting of human chromosomes |journal=Bull Hist Med |volume=48 |issue=4 |pages=465–502 |year=1974 |pmid=4618149 }}</ref> In 1912, [[Hans von Winiwarter]] reported 47 chromosomes in [[spermatogonia]] and 48 in [[oogonia]], concluding an [[XO sex-determination system|XX/XO sex determination]] mechanism.<ref>{{cite journal |author=von Winiwarter H. |title=Études sur la spermatogenèse humaine |journal=Archives de Biologie |volume=27 |issue=93 |pages=147–9 |year=1912 }}</ref> [[Theophilus Painter|Painter]] in 1922 was not certain whether the diploid of humans was 46 or 48, at first favoring 46,<ref>{{cite journal |author=Painter T.S. |title=The spermatogenesis of man |journal=Anat. Res. |volume=23 |page=129 |year=1922 }}</ref> but revised his opinion from 46 to 48, and he correctly insisted on humans having an [[XY sex-determination system|XX/XY]] system.<ref>{{cite journal |author=Painter T.S. |title=Studies in mammalian spermatogenesis II |journal=J. Exp. Zoology |volume=37 |pages=291–336 |year=1923 |doi=10.1002/jez.1400370303 |issue=3 }}</ref> Considering the techniques of the time, these results were remarkable.

[[File:Chromosome2 merge.png|thumb|Fusion of ancestral chromosomes left distinctive remnants of telomeres, and a vestigial centromere]]

[[Joe Hin Tjio]] working in [[Albert Levan]]'s lab<ref>{{cite news|url=https://www.theguardian.com/news/2001/dec/11/guardianobituaries.medicalscience|title=Joe Hin Tjio The man who cracked the chromosome count|newspaper=[[The Guardian]]|first=Pearce |last=Wright |date=11 December 2001}}</ref> found the chromosome count to be 46 using new techniques available at the time:

# Using cells in [[tissue culture]]
# Pretreating cells in a [[Tonicity#Hypotonicity|hypotonic solution]], which swells them and spreads the chromosomes
# Arresting [[mitosis]] in [[metaphase]] by a solution of [[colchicine]]
# Squashing the preparation on the slide forcing the chromosomes into a single plane
# Cutting up a photomicrograph and arranging the result into an indisputable karyogram.

The work took place in 1955, and was published in 1956. The karyotype of humans includes only 46 chromosomes.<ref>{{cite journal |author1=Tjio J.H. |author2=Levan A. |title=The chromosome number of man |journal=Hereditas |volume=42 |issue=1–2 |pages=1–6 |year=1956 |doi=10.1111/j.1601-5223.1956.tb03010.x |pmid=345813 |doi-access=free }}</ref><ref name="Hsu">Hsu T.C. 1979. ''Human and mammalian cytogenetics: a historical perspective''. Springer-Verlag, NY.</ref> The other [[great apes]] have 48 chromosomes. [[Human chromosome 2]] is now known to be a result of an end-to-end fusion of two ancestral ape chromosomes.<ref name="fusion">[http://www.evolutionpages.com/chromosome_2.htm Human chromosome 2 is a fusion of two ancestral. chromosomes] Alec MacAndrew; accessed 18 May 2006.</ref><ref>[https://www.youtube.com/watch?v=x-WAHpC0Ah0 Evidence of common ancestry: human chromosome 2] (video) 2007</ref>