GENE FLOW AND SELECTION To address the combined effects of gene flow and selection, we will invoke a "fight" similar to what we described for mutation selection balance above. Consider that some weak allele is wafting over to the other side of the tracks, so to speak, where they do not survive (e.g., fish swimming into New York harbor). There is an evolutionary pressure changing allele frequencies in one direction ( into the harbor), and an opposing evolutionary force eliminating those alleles (sewage killing off genetically intolerant fish). Depending on the relative strengths of these two opposing forces, an equilibrium condition can arise. Lets consider the movement of the "a" allele, and assume that it is completely recessive in its phenotype of death-by-sewage. The change in allele frequency from the migration into the harbor can be defined as above: ∆ q = -m(q x t- q y t ) . (Note that we have changed p to q since we are considering the a allele; x and y refer to the two populations). The change in allele frequency due to selection against this allele is
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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.