Laserfiche WebLink
similar genetic character, based on allele frequencies at neutral markers, to reflect an adequate <br />statistical sample of the genome (Allendorf and Phelps 1981; Pearman 2001; and Milligan et al. <br />1994). <br />Loss of adaptive variation by random genetic drift <br />Loss of within population diversity due to the effects of genetic drift is a common event <br />associated with small populations (Lande 1995). Random -genetic drift typically occurs in nature <br />in marginal habitat, where populations are small, and conditions suboptimal. This change in <br />genome is again associated with sampling error. In this instance, a few individuals will contribute <br />to the next generation by chance and not as a result of Darwinian selection. The genetic changes <br />are similar to a founding effect, although it is more appropriate to say that genetic drift is typically <br />subsequent to a founding event. Drift is of particular concern when populations are small, such as <br />some hatchery broodstocks, and too few individuals are used to contribute to the next generation. <br />It is incumbent on managers of captive stocks to ensure that population size is large enough, and <br />progeny produced contain a large enough sample of the available genome to overcome the effects <br />of random genetic drift. <br />Inbreeding and inbreeding depression <br />Inbreeding is correlated with population size. Mating of related individuals can lead to <br />altered genetic structure in small populations. Larger populations contain more individuals, and <br />the chance of mating by individuals that are not related is statistically greater (Blouin et al. 1996). <br />Inbreeding does not lead to a reduction in allelic diversity, but to the partitioning of alleles into <br />homozygotes at the expense of heterozygotes (Lynch et al. 1999). Matings between relatives is <br />not necessarily bad; inbreeding is a problem only when it results in inbreeding depression. <br />25