Genetic structure of American chestnut populations based on neutral DNA markers
Microsatellite and RAPD markers suggest that American chestnut exists as a highly variable species. Even at the margins of its natural range, with a large proportion of its genetic variability occurring within populations (~95%). A statistically significant proportion also exists among population. Although genetic differentiation among populations has taken place, no disjunct regional pattern of variation exists. A cline in allele frequencies and number of rare alleles occurrs along the Appalachian axis, with the highest levels of gene diversity and the greatest numbers of rare alleles being found in southwestern populations. Population pairwise estimates of genetic distance are significantly associated with the geographic distance between populations. Geographically proximate populations are slightly more genetically similar than geographically distant populations. Genetic variability in American chestnut follows a pattern consistent with the hypothesis of a single metapopulation in which genetic drift plays a major evolutionary role. Results of this study are based on neutral genetic loci and do not necessarily reflect genetic differentiation for adaptive genes or gene complexes. Therefore, in order to assure that most of the variation at the genes is also captured in conservation and breeding endeavors, sampling should focus on collecting a fairly large number of individuals from each of several geographic areas
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