Gene flow

Gene flow is the transfer of alleles from one population to another through the movement, or migration, of individuals between them, sometimes called migration or allele flow in population genetics. Because it moves genetic material between populations, gene flow directly reshapes their genetic makeup; research has found that as little as one migrant per generation can be enough to prevent populations from diverging through genetic drift, although sufficiently strong selection can still drive divergence even while alleles continue to move between groups. High rates of gene flow reduce genetic differentiation between populations and increase their overall similarity by evening out allele frequencies, while gene flow more broadly constrains speciation by continually mixing the gene pools of different groups and preventing the buildup of differences that would otherwise lead populations to adapt and diverge; geographic isolation and other barriers that limit gene flow instead create the conditions under which speciation can proceed.