Editing Genetic linkage (section)

==Linkage map==
[[File:Drosophila Gene Linkage Map.svg|thumb|500px|[[Thomas Hunt Morgan|Thomas Hunt Morgan's]] ''[[Drosophila melanogaster]]'' genetic linkage map. This was the first successful [[gene mapping]] work and provides important evidence for the [[chromosome theory of inheritance]]. The map shows the relative positions of [[alleles]] on the second ''Drosophila'' chromosome. The distances between the genes ([[centimorgans]]) are equal to the percentages of [[chromosomal crossover]] events that occur between different alleles.<ref>{{Cite book |last=Mader |first=Sylvia |title=Biology Ninth Edition |date=2007 |publisher=McGraw-Hill |isbn=978-0-07-325839-3 |location=New York |page=209}}</ref>]]
{{See also|Gene map}}

A '''linkage map''' (also known as a '''genetic map''') is a table for a species or experimental population that shows the position of its known [[genes]] or [[genetic markers]] relative to each other in terms of recombination frequency, rather than a specific physical distance along each chromosome. Linkage maps were first developed by [[Alfred Sturtevant]], a student of [[Thomas Hunt Morgan]].{{cn|date=December 2024}}

A linkage map is a map based on the frequencies of [[homologous recombination|recombination]] between markers during [[chromosomal crossover|crossover]] of [[homologous chromosome]]s. The greater the frequency of recombination (segregation) between two genetic markers, the further apart they are assumed to be. Conversely, the lower the frequency of recombination between the markers, the smaller the physical distance between them. Historically, the markers originally used were detectable [[phenotype]]s (enzyme production, eye colour) derived from [[Coding DNA sequence|coding DNA]] sequences; eventually, confirmed or assumed [[noncoding DNA]] sequences such as [[Microsatellite (genetics)|microsatellites]] or those generating restriction fragment length polymorphisms ([[RFLP]]s) have been used.{{cn|date=December 2024}}

{{anchor|linkage group}}Linkage maps help researchers to locate other markers, such as other genes by testing for genetic linkage of the already known markers.  In the early stages of developing a linkage map, the data are used to assemble '''linkage groups''', a set of genes which are known to be linked. As knowledge advances, more markers can be added to a group, until the group covers an entire chromosome.<ref>{{Cite book |last=Griffiths |first=AJF |url=https://www.ncbi.nlm.nih.gov/books/NBK21878/ |title=An Introduction to Genetic Analysis |date=2000 |publisher=W. H. Freeman |edition=7th}}</ref> For well-studied organisms the linkage groups correspond one-to-one with the chromosomes.{{cn|date=December 2024}}

A linkage map is '''not''' a physical map (such as a [[radiation reduced hybrid]] map) or [[gene map]].{{cn|date=December 2024}}