Gene Flow

Gene flow is the movement of genes from one population of a species into another. It works

against speciation, as separate populations cannot genetically differentiate if migrant genes are passed between populations. It is a homogenising force. The absence of gene flow, due to reproductive isolation, plays a key role in speciation.

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Gene flow may be due to the movement of gametes, extinction and recolonisation of entire populations or the movement of extracellular segments of DNA. Gene flow along with other evolutionary mechanisms show the genetic identity of a population but its effects may be overcame by strong natural selection which proposes differentiation of species.

Each genetic locus can be ruled by different selective pressures. Some loci spread by gene flow can show little geographic distribution, while others can show huge distribution. This is why neutral alleles are the ideal tool to investigate rates of gene flow - they are not governed by external pressure and so their distribution is a reflection of the actual gene flow that is occurring. Gene flow is generally linked with dispersal, the movement of entire organisms. Dispersal characteristics may be investigated when examining gene flow, but they often do not match up with expected gene flow, due to selective pressures. Gene flow may also occur via other means such as wind dispersal, as seeds are transported by the wind or through animals. It may occur within a species, or between species, called horizontal gene transfer.

The relationship between genetic uniformity and gene flow may be observed in the pocillopora dormicans. In the Tropical Eastern Pacific (TEP) the populations are some of the most isolated in the world due to the Eastern Pacific Barrier, a 5000 km stretch at open seen named “impossible” for tropical shelf fauna by Darwin. However, there remains some transpacific species. Guzman et al (2008) showed huge genetic differentiation between P. dormicans of the central west pacific...