DRIFT AND GENE FLOW - migration can be estimated from the...

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DRIFT AND GENE FLOW Gene flow can counteract the loss of heterozygosity due to drift as well as counteract the random divergence of allele frequencies among populations. The balance between these two opposing forces can be described by an equation for the equilibrium variance among populations V (among pops.) Å . As m increases, the variance decreases (faster homogenization); as N e increases, the variance decreases (drift acts more slowly with larger N e ). Major conclusion is that it takes very little gene flow to keep two "populations" homogeneous, as little as one reproductive migrant between populations per generation! See figure 5.13, pg. 128. A number of different methods have been developed to estimate migration rates from standing patterns of allele frequency variation. This rests on the fact that Fst values are a result of a "balance" between gene flow and drift. One can calculate Fst from molecular markers, and if an estimate of effective population size is available,
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Unformatted text preview: migration can be estimated from the following relation: Fst Å 1/(4N e m + 1 ). By rearranging the formula and plugging in trial values you can see that low values for m result in high values for Fst, and high values of m give low values of Fst. This follows from the homogenizing effect of gene flow on allele frequency variation among populations. The nature of population differentiation can depend on population structure . Typical scenarios include a Continent-Island model (gene flow from continent to island), an Island model (equal probability of gene flow among several/many populations), Stepping Stone model (gene flow is sequential among populations), Continuous Model (e.g., carpet of individuals). In all cases (except Island model) there can be Isolation by Distance simply reflecting incomplete homogenization of populations due to incomplete flow of genes among all populations....
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This note was uploaded on 11/05/2011 for the course BIOLOGY MCB2010 taught by Professor Jessicadigirolamo during the Fall '10 term at Broward College.

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