Editing Chromosomal crossover (section)

== History of discovery ==
Crossing over was described, in theory, by [[Thomas Hunt Morgan]]; the term crossover was coined by Morgan and Eleth Cattell.<ref>{{Cite journal | vauthors = Morgan TH, Cattell E |date=1912 |title=Data for the study of sex-linked inheritance in Drosophila |journal=Journal of Experimental Zoology | issue = 1 |volume=13  |pages=79–101|doi=10.1002/jez.1400130105 |bibcode=1912JEZ....13...79M |url=https://zenodo.org/record/2153714 }}</ref> Hunt relied on the discovery of [[Frans Alfons Janssens]] who described the phenomenon in 1909 and had called it "chiasmatypie".<ref>{{cite journal | vauthors = Janssens FA, Koszul R, Zickler D | title = The chiasmatype theory. A new interpretation of the maturation divisions. 1909 | journal = Genetics | volume = 191 | issue = 2 | pages = 319–346 | date = June 2012 | pmid = 22701051 | pmc = 3374304 | doi = 10.1534/genetics.112.139725 }}</ref> The term ''[[chiasma (genetics)|chiasma]]'' is linked, if not identical, to chromosomal crossover. Morgan immediately saw the great importance of Janssens' cytological interpretation of chiasmata to the experimental results of his research on the heredity of ''[[Drosophila]]''. The physical basis of crossing over was first demonstrated by [[Harriet Creighton]] and [[Barbara McClintock]] in 1931.<ref>{{cite journal | vauthors = Creighton HB, McClintock B | title = A Correlation of Cytological and Genetical Crossing-Over in Zea Mays | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 17 | issue = 8 | pages = 492–497 | date = August 1931 | pmid = 16587654 | pmc = 1076098 | doi = 10.1073/pnas.17.8.492 | doi-access = free | bibcode = 1931PNAS...17..492C }} (Original paper)</ref>

The linked frequency of crossing over between two [[gene]] loci ([[genetic marker|markers]]) is the ''[[crossing-over value]]''. For fixed set of genetic and environmental conditions, [[genetic recombination|recombination]] in a particular region of a linkage structure ([[chromosome]]) tends to be constant and the same is then true for the crossing-over value which is used in the production of [[genetic map]]s.<ref name="RM">{{cite book | vauthors = Rieger R, Michaelis A, Green MM |year=1976 |title=Glossary of genetics and cytogenetics: Classical and molecular |publisher=Springer-Verlag |place=Heidelberg – New York |isbn=978-3-540-07668-1}}</ref><ref>{{cite book | vauthors = King RC, Stransfield WD |year=1998 |title=Dictionary of genetics |publisher=Oxford University Press |place=New York & Oxford |isbn=0-19-50944-1-7}} {{ISBN|0-19-509442-5}}.</ref>

When Hotta et al. in 1977 compared [[meiosis|meiotic]] crossing-over ([[genetic recombination|recombination]]) in lily and mouse they concluded that diverse [[eukaryote]]s share a common pattern.<ref>{{cite journal | vauthors = Hotta Y, Chandley AC, Stern H | title = Meiotic crossing-over in lily and mouse | journal = Nature | volume = 269 | issue = 5625 | pages = 240–242 | date = September 1977 | pmid = 593319 | doi = 10.1038/269240a0 | s2cid = 4268089 | bibcode = 1977Natur.269..240H }}</ref> This finding suggested that chromosomal crossing over is a general characteristic of eukaryotic meiosis.