Editing Gene flow (section)

{{Short description|Transfer of genetic variation from one population to another}}
[[File:Gene flow final.png|right|thumb|upright=1.35|Gene flow is the transfer of [[allele]]s from one [[population]] to another population through immigration of individuals.]]
In [[population genetics]], '''gene flow''' (also known as '''migration''' and '''[[allele]] flow''') is the transfer of [[genetic variation|genetic]] material from one [[population]] to another.  If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population. It has been shown that it takes only "one migrant per generation"  to prevent populations from diverging due to [[Genetic drift|drift]].<ref name=":0">{{Cite book|url=https://books.google.com/books?id=F-XB8hqZ4s8C&q=conservation+genetics&pg=PR13|title=Introduction to Conservation Genetics|last1=Frankham|first1=Richard|last2=Briscoe|first2=David A.|last3=Ballou|first3=Jonathan D. | name-list-style = vanc |date=2002-03-14|publisher=Cambridge University Press|isbn=9780521639859|language=en}}</ref> Populations can diverge due to [[Natural selection|selection]] even when they are exchanging alleles, if the selection pressure is strong enough.<ref>{{cite journal | vauthors = Stankowski S | title = Ecological speciation in an island snail: evidence for the parallel evolution of a novel ecotype and maintenance by ecologically dependent postzygotic isolation | journal = Molecular Ecology | volume = 22 | issue = 10 | pages = 2726–41 | date = May 2013 | pmid = 23506623 | doi = 10.1111/mec.12287 | bibcode = 2013MolEc..22.2726S | s2cid = 39592922 | url = https://onlinelibrary.wiley.com/doi/abs/10.1111/mec.12287 | url-access = subscription }}</ref><ref>{{Cite journal| vauthors = Gemmell MR, Trewick SA, Crampton JS, Vaux F, Hills SF, Daly EE, Marshall BA, Beu AG, Morgan-Richards M |date=2018-11-26|title=Genetic structure and shell shape variation within a rocky shore whelk suggest both diverging and constraining selection with gene flow |journal=Biological Journal of the Linnean Society|language=en|volume=125|issue=4|pages=827–843|doi=10.1093/biolinnean/bly142|issn=0024-4066|doi-access=free}}</ref> Gene flow is an important mechanism for transferring genetic diversity among populations.  Migrants change the distribution of genetic diversity among populations, by modifying [[allele frequencies]] (the proportion of members carrying a particular variant of a gene). High rates of gene flow can reduce the genetic differentiation between the two groups, increasing homogeneity.<ref name=":1" /> Gene flow has been thought to constrain [[speciation]] and prevent range expansion by combining the gene pools of the groups, thus preventing the development of differences in genetic variation that would have led to differentiation and [[adaptation]] for this reason.<ref>{{cite journal | vauthors = Bolnick DI, Nosil P | title = Natural selection in populations subject to a migration load | journal = Evolution; International Journal of Organic Evolution | volume = 61 | issue = 9 | pages = 2229–43 | date = September 2007 | pmid = 17767592 | doi = 10.1111/j.1558-5646.2007.00179.x | s2cid = 25685919 | doi-access =  }}</ref> In some cases dispersal resulting in gene flow may also result in the addition of novel genetic variants under positive selection to the [[gene pool]] of a species or population (adaptive introgression.<ref>{{cite journal | vauthors = Song Y, Endepols S, Klemann N, Richter D, Matuschka FR, Shih CH, Nachman MW, Kohn MH | display-authors = 6 | title = Adaptive introgression of anticoagulant rodent poison resistance by hybridization between old world mice | journal = Current Biology | volume = 21 | issue = 15 | pages = 1296–301 | date = August 2011 | pmid = 21782438 | pmc = 3152605 | doi = 10.1016/j.cub.2011.06.043 | bibcode = 2011CBio...21.1296S }}</ref>)

There are a number of factors that affect the rate of gene flow between different populations. Gene flow is expected to be lower in species that have low dispersal or mobility, that occur in fragmented habitats, where there is long distances between populations, and when there are small population sizes.<ref>{{cite journal | vauthors = Hastings A, Harrison S |title=Metapopulation Dynamics and Genetics |journal=Annual Review of Ecology and Systematics |date=November 1994 |volume=25 |issue=1 |pages=167–188 |doi=10.1146/annurev.es.25.110194.001123 |bibcode=1994AnRES..25..167H }}</ref><ref>{{cite journal |title=Effects of life history traits on genetic diversity in plant species |journal=Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences |date=January 1997 |volume=351 |issue=1345 |pages=1291–1298 |doi=10.1098/rstb.1996.0112 }}</ref> Mobility plays an important role in dispersal rate, as highly mobile individuals tend to have greater movement prospects.<ref>{{Cite journal |last1=Cunningham |first1=Charles |last2=Parra |first2=Jorge E |last3=Coals |first3=Lucy |last4=Beltrán |first4=Marcela |last5=Zefania |first5=Sama |last6=Székely |first6=Tamás |date=2018 |title=Social interactions predict genetic diversification: an experimental manipulation in shorebirds |url=https://academic.oup.com/beheco/article/29/3/609/4858583 |journal=Behavioral Ecology |language=en |volume=29 |issue=3 |pages=609–618 |doi=10.1093/beheco/ary012 |issn=1045-2249 |pmc=5946871 |pmid=29769794}}</ref> Although animals are thought to be more mobile than plants, pollen and seeds may be carried great distances by animals, water or wind. When gene flow is impeded, there can be an increase in [[inbreeding]], measured by the [[Inbreeding Coefficient|inbreeding coefficient]] (F) within a population. For example, many island populations have low rates of gene flow due to geographic isolation and small population sizes. The [[Black-footed Rock-wallaby|Black Footed Rock Wallaby]] has several inbred populations that live on various islands off the coast of Australia. The population is so strongly isolated that lack of gene flow has led to high rates of inbreeding.<ref name="EldridgeKing1999">{{cite journal | vauthors = Eldridge MD, King JM, Loupis AK, Spencer PB, Taylor AC, Pope LC, Hall GP |title=Unprecedented Low Levels of Genetic Variation and Inbreeding Depression in an Island Population of the Black-Footed Rock-Wallaby |journal=Conservation Biology |date=June 1999 |volume=13 |issue=3 |pages=531–541 |doi=10.1046/j.1523-1739.1999.98115.x |bibcode=1999ConBi..13..531E |s2cid=85948161 }}</ref>