Editing Gene flow (section)

== Measuring gene flow ==
The level of gene flow among populations can be estimated by observing the dispersal of individuals and recording their reproductive success.<ref name=":1">{{Cite journal|last=Slatkin|first=Montgomery|date=1987|title=Gene Flow and the Geographic Structure of Natural Populations|url=https://www.jstor.org/stable/1699930|journal=Science|volume=236|issue=4803|pages=787–792|doi=10.1126/science.3576198|jstor=1699930|pmid=3576198|bibcode=1987Sci...236..787S |issn=0036-8075|url-access=subscription}}</ref><ref name=":2">{{cite journal | vauthors = Adams JR, Vucetich LM, Hedrick PW, Peterson RO, Vucetich JA | title = Genomic sweep and potential genetic rescue during limiting environmental conditions in an isolated wolf population | journal = Proceedings. Biological Sciences | volume = 278 | issue = 1723 | pages = 3336–44 | date = November 2011 | pmid = 21450731 | pmc = 3177630 | doi = 10.1098/rspb.2011.0261 }}</ref> This direct method is only suitable for some types of organisms, more often indirect methods are used that infer gene flow by comparing allele frequencies among population samples.<ref name=":0" /><ref name=":1" /> The more genetically differentiated two populations are, the lower the estimate of gene flow, because gene flow has a homogenizing effect.  Isolation of populations leads to divergence due to drift, while migration reduces divergence. Gene flow can be measured by using the [[effective&nbsp;population size]] (<math>N_e</math>) and the net migration rate per generation (m). Using the approximation based on the Island model, the effect of migration can be calculated for a population in terms of the degree of genetic differentiation(<math>F_{ST}</math>).<ref>{{cite book |last1=Neigel |first1=Joseph E. |chapter=Estimation of Effective Population Size and Migration Parameters From Genetic Data |pages=329–346 |chapter-url={{Google books|QI8sdCHszY0C|pages=329|plainurl=yes}} |editor1-last=Smith |editor1-first=Thomas B. |editor2-last=Wayne |editor2-first=Robert K.  | name-list-style = vanc |title=Molecular Genetic Approaches in Conservation |date=1996 |publisher=Oxford University Press |isbn=978-0-19-534466-0 }}</ref> This formula accounts for the proportion of total [[molecular marker]] variation among populations, averaged over [[locus (genetics)|loci]].<ref>Rogers, D. L., & Montalvo, A. M. (2004). Genetically appropriate choices for plant materials to maintain biological diversity. University of California. Report to the USDA Forest Service, Rocky Mountain Region, Lakewood, CO.&nbsp;''www. f s I ed. u s/ r'',&nbsp;''2''.</ref>  When there is one migrant per generation, the inbreeding coefficient (<math>F_{ST}</math>) equals 0.2. However, when there is less than 1 migrant per generation (no migration), the inbreeding coefficient rises rapidly resulting in fixation and complete divergence (<math>F_{ST}</math> = 1). The most common <math>F_{ST}</math> is < 0.25. This means there is some migration happening. Measures of population structure range from 0 to 1. When gene flow occurs via migration the deleterious effects of inbreeding can be ameliorated.<ref name=":0" />

<math>F_{ST} = 1/(4N_em +1)</math>

The formula can be modified to solve for the migration rate when <math>F_{ST}</math> is known: <math>Nm= ((1/F_{ST})-1)/4 = \tfrac{1 - F_{ST}}{4 * F_{ST}}</math>, Nm = number of migrants.<ref name=":0" />