Gene flow - wikipedia Gene flow Gene flow is the transfer of alleles from one population to another population through immigration of individuals. In population genetics, gene flow ( also known as gene migration or allele flow ) is the transfer of genetic variation from one population to another. If the rate of gene flow is high enough, then two populations are considered to have equivalent genetic diversity and therefore effectively be a single population. It has been shown that it takes only `` One migrant per generation '' to prevent populations from diverging due to drift. Gene flow is an important mechanism for transferring genetic diversity among populations. Migrants change the distribution of genetic diversity within the populations, by modifying the 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. For this reason, gene flow has been thought to constrain speciation by combining the gene pools of the groups, thus preventing the development of differences in genetic variation that would have led to full speciation. In some cases migration may also result in the addition of novel genetic variants to the gene pool of a species or population. 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. Mobility plays an important role in the migration rate, as highly mobile individuals tend to have greater migratory prospects. Although animals are thought to be more mobile than plants, pollen and seeds may be carried great distances by animals or wind. When gene flow is impeded, there can be an increase in inbreeding, measured by the 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 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. Contents 1 Measuring gene flow 2 Barriers to gene flow 2.1 Allopatric speciation 2.2 Sympatric speciation 3 Human assisted gene - flow 3.1 Genetic rescue 3.2 Genetic pollution 4 Gene flow between species 4.1 Horizontal gene transfer 4.2 Hybridization 5 Examples 6 See also 7 References 8 External links Measuring gene flow Decrease in population size leads to increased divergence due to drift, while migration reduces divergence and inbreeding. Gene flow can be measured by using the effective population size ( N e ( displaystyle N_ ( e ) ) ) 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 ( F s t ( displaystyle Fst ) ). This formula accounts for the proportion of total molecular marker variation among populations, averaged over loci. When there is one migrant per generation, the inbreeding coefficient ( F s t ( displaystyle Fst ) ) 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 ( F s t ( displaystyle Fst ) = 1 ). The most common F s t ( displaystyle Fst ) 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. F s t = 1 / ( 4 N e m + 1 ) ( displaystyle Fst = 1 / ( 4N_ ( e ) m + 1 ) ) The formula can be modified to solve for the migration rate when F s t ( displaystyle Fst ) is known : N m = 1 ( 1 / F s t − 1 ) / 4 ( displaystyle Nm = 1 ( 1 / Fst - 1 ) / 4 ), Nm = number of migrants. Barriers to gene flow Allopatric speciation Examples of speciation affecting gene flow. When gene flow is blocked by physical barriers, this results in Allopatric speciation or a geographical isolation that does not allow populations of the same species to exchange genetic material. Physical barriers to gene flow are usually, but not always, natural. They may include impassable mountain ranges, oceans, or vast deserts. In some cases, they can be artificial, man - made barriers, such as the Great Wall of China, which has hindered the gene flow of native plant populations. One of these native plants, Ulmus pumila, demonstrated a lower prevalence of genetic differentiation than the plants Vitex negundo, Ziziphus jujuba, Heteropappus hispidus, and Prunus armeniaca whose habitat is located on the opposite side of the Great Wall of China where Ulmus pumila grows. This is because Ulmus pumila has wind - pollination as its primary means of propagation and the latter - plants carry out pollination through insects. Samples of the same species which grow on either side have been shown to have developed genetic differences, because there is little to no gene flow to provide recombination of the gene pools. Sympatric speciation Barriers to gene flow need not always be physical. Sympatric speciation happens when new species from the same ancestral species arise along the same range. This is often a result of a reproductive barrier. For example, two palm species of Howea found on Lord Howe Island were found to have substantially different flowering times correlated with soil preference, resulting in a reproductive barrier inhibiting gene flow. Species can live in the same environment, yet show very limited gene flow due to reproductive barriers, fragmentation, specialist pollinators, or limited hybridization or hybridization yielding unfit hybrids. A cryptic species is a species that humans can not tell is different without the use of genetics. Moreover, gene flow between hybrid and wild populations can result in loss of genetic diversity via genetic pollution, assortative mating and outbreeding. Human assisted gene - flow Genetic Rescue Gene flow can also be used to assist species which are threatened with extinction. When a species exist in small populations there is an increased risk of inbreeding and greater susceptibility to loss of diversity due to drift. These populations can benefit greatly from the introduction of unrelated individuals who can increase diversity and reduce the amount of inbreeding, and thus increase overall fitness. This was demonstrated in the lab with two bottleneck strains of drosophila melanogaster, in which crosses between the two populations reversed the effects of inbreeding and led to greater chances of survival in not only one generation but two. Genetic pollution Main article : Genetic pollution Human activities such as movement of species and modification of landscape can result in genetic pollution, hybridization, introgression and genetic swamping. These processes can lead to homogenization or replacement of local genotypes as a result of either a numerical and / or fitness advantage of introduced plant or animal. Nonnative species can threaten native plants and animals with extinction by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones which can occur between island and mainland species. Interbreeding between the species can cause a ' swamping ' of the rarer species ' gene pool, creating hybrids that supplant the native stock. This is a direct result of evolutionary forces such as natural selection, as well as genetic drift, which lead to the increasing prevalence of advantageous traits and homogenization. The extent of this phenomenon is not always apparent from outward appearance alone. While some degree of gene flow occurs in the course of normal evolution, hybridization with or without introgression may threaten a rare species ' existence. For example, the Mallard is an abundant species of duck that interbreeds readily with a wide range of other ducks and poses a threat to the integrity of some species. Gene flow between species Horizontal gene transfer Main article : Horizontal gene transfer Horizontal gene transfer ( HGT ) refers to the transfer of genes between organisms in a manner other than traditional reproduction, either through transformation ( direct uptake of genetic material by a cell from its surroundings ), conjugation ( transfer of genetic material between two bacterial cells in direct contact ), transduction ( injection of foreign DNA by a bacteriophage virus into the host cell ) or GTA - mediated transduction ( transfer by a virus - like element produced by a bacterium ). Viruses can transfer genes between species. Bacteria can incorporate genes from dead bacteria, exchange genes with living bacteria, and can exchange plasmids across species boundaries. `` Sequence comparisons suggest recent horizontal transfer of many genes among diverse species including across the boundaries of phylogenetic ' domains '. Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes. '' Biologist Gogarten suggests `` the original metaphor of a tree no longer fits the data from recent genome research ''. Biologists ( should ) instead use the metaphor of a mosaic to describe the different histories combined in individual genomes and use the metaphor of an intertwined net to visualize the rich exchange and cooperative effects of horizontal gene transfer. `` Using single genes as phylogenetic markers, it is difficult to trace organismal phylogeny in the presence of HGT. Combining the simple coalescence model of cladogenesis with rare HGT events suggest there was no single last common ancestor that contained all of the genes ancestral to those shared among the three domains of life. Each contemporary molecule has its own history and traces back to an individual molecule cenancestor. However, these molecular ancestors were likely to be present in different organisms at different times. '' Hybridization In some instances, when a species has a sister species and breeding capabilities are possible due to the removal of previous barriers or through introduction due to human intervention, species can hybridize and exchange genes and corresponding traits. This exchange is not always clear - cut, for sometimes the hybrids may look identical to the original species phenotypically but upon testing the mtDNA it is apparent that hybridization has occurred. Differential hybridization also occurs because some traits and DNA are more readily exchanged than others, and this is a result of selective pressure or the absence thereof that allows for easier transaction. In instances in which the introduced species begins to replace the native species, the native species becomes threatened and the biodiversity is reduced, thus making this phenomenon negative rather than a positive case of gene flow that augments genetic diversity. Introgression is the term used to describe the replacement of the native species genes with that of the invader species. It is important to note that hybrids are generally deemed less `` fit '' than their parental generation, and as a result is a closely monitored genetic issue as the ultimate goal in conservation genetics is to maintain the genetic integrity of a species and preserve biodiversity. Examples Marine iguana of the Galapagos Islands evolved via allopatric speciation, through limited gene flow and geographic isolation. While gene flow can greatly enhance the fitness of a population, it can also have negative consequences depending on the population and the environment in which they reside. The effects of gene flow are context - dependent. Fragmented Population : fragmented landscapes such as the Galapagos Islands are an ideal place for adaptive radiation to occur as a result of differing geography. Darwin 's Finches likely experienced allopatric speciation in some part due to differing geography, but that does n't explain why we see so many different kinds of finches on the same island. This is due to adaptive radiation, or the evolution of varying traits in light of competition for resources. Gene flow moves in the direction of what resources are abundant at a given time. Island Population : The Marine Iguana is en endemic species of the Galapagos Islands, but it evolved from a mainland ancestor of land iguana. Due to geographic isolation gene flow between the two species was limited and differing environments caused the Marine Iguana to evolve in order to adapt to the island environment. For instance, they are the only iguana that has evolved the ability to swim. Human Populations : Two theories exist for the human evolution throughout the world. The first is known as the multiregional model in which modern human variation is seen as a product of radiation of Homo erectus out of Africa after which local differentiation led to the establishment of regional population as we see them now. Gene flow plays an important role in maintaining a grade of similarities and preventing speciation. In contrast the single origin theory assumes that there was a common ancestral population originating in Africa of Homo sapiens which already displayed the anatomical characteristics we see today. This theory minimizes the amount of parallel evolution that is needed. Butterflies : Comparisons between sympatric and allopatric populations of Heliconius melpomene, H. cydno, and H. timareta revealed a genome - wide trend of increased shared variation in sympatry, indicative of pervasive interspecific gene flow. Human - mediated gene flow : The captive genetic management of threatened species is one way in which humans attempt to induce gene flow in ex situ situation. One example is the Giant Panda which is part of an international breeding program in which genetic materials are shared between zoological organizations in order to increase genetic diversity in the small populations. As a result of low reproductive success, artificial insemination with fresh / frozen - thawed sperm was developed which increased cub survival rate. A 2014 study found that high levels of genetic diversity and low levels of inbreeding were estimated in the breeding centers. Plants : Two species of Monkeyflowers, mimulus lewsii and mimulus cardinalis, were found to have highly specialized pollinators that acted on major genes resulting in a contribution to the floral evolution and reproductive isolation of these two species. The specialized pollination limited gene flow between the two species, eventually resulting in two different species. Sika deer : Sika deer were introduced into Western Europe, and they reproduce easily with the native red deer. This translocation of Sika deer has led to introgression and there are no longer `` pure '' red deer in the region, and all can be classified as hybrids. Bobwhite quail : Bobwhite quail were translocated from the southern part of the United States to Ontario in order to increase population numbers and game for hunting. The hybrids that resulted from this translocation was less fit than the native population and were not adapted to survived the Northern Winters. See also Biological dispersal Genetic erosion Genetic admixture References ^ Jump up to : Frankham, Richard ; Briscoe, David A. ; Ballou, Jonathan D. ( 2002 - 03 - 14 ). Introduction to Conservation Genetics. Cambridge University Press. ISBN 9780521639859. Jump up ^ Daniel I. Bolnick and Patrik Nosil. `` NATURAL SELECTION IN POPULATIONS SUBJECT TO A MIGRATION LOAD ''. Jump up ^ A Hastings ; Harrison, and S. ( 1994 ). `` Metapopulation Dynamics and Genetics ''. Annual Review of Ecology and Systematics. 25 ( 1 ) : 167 -- 188. doi : 10.1146 / annurev. es. 25.110194. 001123. Jump up ^ Hamrick, J.L. ; Godt, M.J.W. 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Retrieved from http://www.jstor.org/stable/1700885 Jump up ^ Martin, S.H. ; Dasmahapatra, K.K. ; Nadeau, N.J. ; Salazar, C. ; Walters, J.R. ; Simpson, F. ; Jiggins, C.D. ( 2013 ). `` Genome - wide evidence for speciation with gene flow in Heliconius butterflies ''. Genome Research. 23 ( 11 ) : 1817 -- 1828. doi : 10.1101 / gr. 159426.113. PMC 3814882. PMID 24045163. Jump up ^ Shan, Lei ; Hu, Yibo ; Zhu, Lifeng ; Yan, Li ; Wang, Chengdong ; Li, Desheng ; Jin, Xuelin ; Zhang, Chenglin ; Wei, Fuwen ( 2014 - 10 - 01 ). `` Large - Scale Genetic Survey Provides Insights into the Captive Management and Reintroduction of Giant Pandas ''. Molecular Biology and Evolution. 31 ( 10 ) : 2663 -- 2671. doi : 10.1093 / molbev / msu210. Jump up ^ Schemske, Douglas W. ; Bradshaw, H.D. ( 1999 - 10 - 12 ). `` Pollinator preference and the evolution of floral traits in monkeyflowers ( Mimulus ) ''. 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Co-Extra research on gene flow mitigation Transcontainer research on biocontainment SIGMEA research on the biosafety of GMOs Evolutionary biology Evolutionary history of life Index of evolutionary biology articles Introduction Outline of evolution Timeline of evolution Evolution Abiogenesis Adaptation Adaptive radiation Cladistics Coevolution Common descent Convergence Divergence Earliest known life forms Evidence of evolution Extinction Event Gene - centered view Homology Last universal common ancestor Macroevolution Microevolution Origin of life Panspermia Parallel evolution Speciation Taxonomy Population genetics Biodiversity Gene flow Genetic drift Mutation Natural selection Variation Development Canalisation Evolutionary developmental biology Inversion Modularity Phenotypic plasticity Of taxa Birds origin Brachiopods Molluscs Cephalopods Dinosaurs Fish Fungi Insects butterflies Life Mammals cats canids wolves dogs hyenas dolphins and whales horses primates humans lemurs sea cows Plants Reptiles Spiders Tetrapods Viruses influenza Of organs Cell DNA Flagella Eukaryotes symbiogenesis chromosome endomembrane system mitochondria nucleus plastids In animals eye hair auditory ossicle nervous system brain Of processes Aging Death Programmed cell death Avian flight Biological complexity Cooperation Color vision in primates Emotion Empathy Ethics Eusociality Immune system Metabolism Monogamy Morality Mosaic evolution Multicellularity Sexual reproduction Gamete differentiation / sexes Life cycles / nuclear phases Mating types Meiosis Sex - determination Snake venom Tempo and modes Gradualism / Punctuated equilibrium / Saltationism Micromutation / Macromutation Uniformitarianism / Catastrophism Speciation Allopatric Anagenesis Catagenesis Cladogenesis Cospeciation Ecological Hybrid Parapatric Peripatric Reinforcement Sympatric History Renaissance and Enlightenment Transmutation of species Charles Darwin On the Origin of Species History of paleontology Transitional fossil Blending inheritance Mendelian inheritance The eclipse of Darwinism Modern synthesis History of molecular evolution Extended evolutionary synthesis Philosophy Darwinism Alternatives Catastrophism Lamarckism Orthogenesis Mutationism Saltationism Structuralism Spandrel Theistic Vitalism Teleology in biology Related Biogeography Ecological genetics Molecular evolution Phylogenetics Tree Polymorphism Protocell Systematics Commons Portal WikiProject Retrieved from `` https://en.wikipedia.org/w/index.php?title=Gene_flow&oldid=856702677 '' Categories : Population genetics Hidden categories : All articles with dead external links Articles with dead external links from January 2017 Articles with permanently dead external links Talk Contents About Wikipedia Български Català Čeština Dansk Deitsch Deutsch Eesti Ελληνικά Español Esperanto فارسی Français Gaeilge Galego 한국어 Hrvatski Bahasa Indonesia Íslenska Italiano עברית Basa Jawa Magyar Македонски 日本 語 Norsk Oʻzbekcha / ўзбекча Polski Português Русский Simple English Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska ไทย Türkçe Українська Zazaki 中文 31 more Edit links This page was last edited on 27 August 2018, at 01 : 12 ( UTC ). 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Question: two populations that have no gene flow between them are likely to
Answer: have developed genetic differences