Use of Allelic Frequencies to Describe Population Structure

Abstract

Development of electrophoretic techniques has allowed the estimation of allelic frequencies at many isozyme loci in populations of fish. The pattern of allelic frequency divergence in salmonid populations has been used to describe the pattern of genetic exchange and degree of isolation among local geographic units. Our goal is to determine how much genetic exchange among subpopulations will yield observed patterns of allelic divergence. We approach this goal using population genetics theory and a series of computer simulations.The amount of allelic divergence between subpopulations is a function of the absolute number of migrant individuals exchanged, and not the proportion of individuals exchanged. Therefore, some knowledge of population sizes is needed to estimate degree of reproductive isolation from allelic frequency data. Second, statistically significant allelic divergence will often be present even when there is substantial exchange among subpopulations. For example, significant allelic divergence was present in our simulations over 50% of the time with 20 subpopulations exchanging 50 individuals per generation. Third, allelic frequencies estimated from fry should be used with caution when drawing conclusions about the significance of allelic divergence in the reproducing adults.Key words: allelic divergence, reproductive isolation, gene flow, genetic drift, computer simulations