<P> In population genetics, gene flow (also known as gene migration) 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 a single population . It has been shown that it takes only "One migrant per generation" to prevent population diverging due to drift . Gene flow is an important mechanism for transferring genetic diversity among populations . Migrants into or out of a population may result in a change in allele frequencies (the proportion of members carrying a particular variant of a gene), changing the distribution of genetic diversity within the populations . Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population . 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, and thus, preventing the development of differences in genetic variation that would have led to full speciation . </P> <P> 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, occur in fragmented habitats, there is long distant between populations, and smaller populations sizes . Mobility plays an important role in the migration rate as a highly mobile individuals tend to have greater migratory potential . Animals tend to be more mobile than plants, although pollen and seeds may be carried great distances by animals or wind . As dispersal distance decreases, gene flow is impeded and inbreeding, measured by the inbreeding coefficient (F), increases. For example, many island populations have low rates of gene flow due to geographically isolated and small population size . 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 gene flow is not a possibility leading to high occurrences of inbreeding . </P> <P> 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 . </P>

What is an important consequence of gene flow in natural populations