This study seeks to identify genes causing darkening of skin pigmentation in Indigenous Americans following expansion into the New World. As populations migrated from northern into southern latitudes, darker skin was more adaptive as protection against damage from ultra-violet radiation. The search for these genes will be conducted in individuals of admixed European and Indigenous American ancestry from New Mexico, Colorado, Mexico and Colombia where ultra-violet radiation is at high levels. 82 genes associated with variation in skin pigmentation were investigated for evidence of natural selection. In the 12 genes showing the strongest evidence of selection, 48 single nucleotide polymorphisms (SNPs) representing the overall variation in the selection nominated candidate genes will be genotyped in individuals of admixed ancestry. These SNPs show substantial allele frequency differences between the parental populations so the genes responsible for variation in skin pigmentation can be identified by an excess of Indigenous American alleles at that gene in individuals with darker skin. This admixture linkage analysis is especially powerful for studying traits like skin pigmentation which vary substantially between the parental populations because this methodology requires fewer total markers than a standard association study. There is substantial intellectual merit in this study because skin pigmentation is an ideal model for the evolution of complex traits in the fluctuating environments encountered by Indigenous Americans dispersing into the New World. However, previous researchers have largely ignored these populations. An increased understanding of the evolution of skin pigmentation also has broader impacts including understanding the selective pressures causing continuous skin color variation which is often mistakenly thought of as a 'racial' trait. Additionally, forensic researchers are interested in the ability to predict skin color from an unknown DNA sample. Finally, this grant will contribute to the training of a female graduate student, an under-represented group in this field.
