Genetic map function: Difference between revisions

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'''Mapping functions''' in [[genetics]] are functions used to model the relationship between [[Gene mapping|genetic map]] distance (measured in map units or [[Centimorgan|centimorgans]]) between [[Genetic marker|markers]] and [[Genetic recombination|recombination]] frequency between markers. One utility of this is that it allows values to be obtained for genetic distances, which is typically not estimable, from recombination fractions, which typically are.<ref>{{Cite book |last=Broman |first=Karl W. |url=https://www.worldcat.org/title/669122118 |title=A guide to QTL mapping with R/qtl |last2=Sen |first2=Saunak |date=2009 |publisher=Springer |isbn=978-0-387-92124-2 |series=Statistics for biology and health |___location=Dordrecht |pages=14 |oclc=669122118}}</ref>

The simplest mapping function was the '''Morgan Mapping Function''', eponymously devised by [[Thomas Hunt Morgan]]. Other well-known mapping functions include the '''Haldane Mapping Function''', introduced by [[J. B. S. Haldane]] in a 1919 paper titled "The combination of linkage values, and the calculation of distances between the loci of linked factors",<ref>{{Cite journal |last=Haldane |first=J.B.S. |date=1919 |title=The combination of linkage values, and the calculation of distances between the loci of linked factors |url=https://www.ias.ac.in/article/fulltext/jgen/008/04/0299-0309 |journal=Journal of Geneitcs |volume=8 |issue=29 |pages=299–309}}</ref> and the '''Kosambi Mapping Function''' introduced by [[Damodar Dharmananda Kosambi]] in 1944.<ref>{{Cite journal |last=Kosambi |first=D. D. |date=1943 |title=THE ESTIMATION OF MAP DISTANCES FROM RECOMBINATION VALUES |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1469-1809.1943.tb02321.x |journal=Annals of Eugenics |language=en |volume=12 |issue=1 |pages=172–175 |doi=10.1111/j.1469-1809.1943.tb02321.x |issn=2050-1420}}</ref><ref name=":0">{{Cite book |last=Wu |first=Rongling |url=https://www.google.ca/books/edition/Statistical_Genetics_of_Quantitative_Tra/-NlGKOEQuEsC?hl=en&gbpv=1&dq=haldane%20mapping%20function&pg=PA65&printsec=frontcover |title=Statistical genetics of quantitative traits: linkage, maps, and QTL |last2=Ma |first2=Chang-Xing |last3=Casella |first3=George |date=2007 |publisher=Springer |isbn=978-0-387-20334-8 |___location=New York |pages=65 |oclc=141385359}}</ref>

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=== Overview ===

The Kosambi mapping function was introduced to account for the impact played by [[crossover interference]] on recombination frequency. It introduces a parameter C, representing the [[coefficient of coincidence]], and sets it equal to 2r. For loci which are strongly [[Linkage disequilibrium|linked]], interference is strong; otherwise, interference decreases towards zero.<ref name=":1" /> Interference declines according to the linear function i = 1 - 2r.<ref name=":2">{{Cite book |last=Hartl |first=Daniel L. |url=https://www.google.ca/books/edition/Genetics/cfvILxY9tCIC?hl=en&gbpv=1&dq=haldane%20mapping%20function&pg=PA168&printsec=frontcover |title=Genetics: analysis of genes and genomes |last2=Jones |first2=Elizabeth W. |date=2005 |publisher=Jones and Bartlett |isbn=978-0-7637-1511-3 |edition=7th |___location=Sudbury, Mass. |pages=168}}</ref>

=== Formula ===

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== Comparing mapping functions ==

Below 10% recombination frequency, there is little mathematical difference between different mapping functions and the relationship between map distance and recombination frequency is linear (that is, 1 map unit = 1% recombination frequency).<ref name=":2" /> While many mapping functions now exist,<ref>{{Cite journal |last=Crow |first=J F |date=1990 |title=Mapping functions. |url=https://academic.oup.com/genetics/article/125/4/669/6000769 |journal=Genetics |language=en |volume=125 |issue=4 |pages=669–671 |doi=10.1093/genetics/125.4.669 |issn=1943-2631 |pmc=PMC1204092 |pmid=2204577}}</ref> in practice functions other than Haldane and Kosambi are rarely used.<ref name=":1" />

== References ==