Characterizing Genetic Drift and Migration between Populations

Abstract

Genetic drift and migration are two of the main mechanisms of evolution at the genetic level. These mechanisms greatly impact the genetic relatedness of populations. Therefore, by studying how genetic drift and migration impact populations, it is possible to reconstruct elements of population history throughout a geographic region. This thesis examines how genetic drift and migration rapidly impact human population structure. My first aim studies the peopling of the Peruvian region and models migration patterns. Here, I suggest that the peopling of Peru was a rapid process that occurred by 12,000 years ago. Furthermore, migration modeling suggests that the majority of migration in Peru is from populations in the high altitude Andes Mountains to the low altitude coast and Amazon. My second aim, then analyzes genetic drift and migration on the fatty acid desaturase gene region, where there is a suggestion of a public health problem due to the apparent fixation of the low efficient ancestral haplogroup in Native Americans. I confirm the near fixation of the ancestral haplogroup in Native American ancestry, and suggest that understanding the frequency of the ancestral haplogroup in the Native American founding population is crucial for determining how this apparently detrimental haplogroup reached near fixation. Furthermore, I suggest that the global distribution of the haplogroup is not indicative of Neanderthal introgression and is instead likely an ancient polymorphism that arose during the divergence of modern humans and Neanderthals. For my final aim, I use rare variant and haplotype based approaches to discern the population structure and evolutionary history of Samoans. I suggest that the early population size was small and a strong population expansion occurred approximately 35 generations ago, consistent with the Samoan archaeological record. In addition, Samoan population structure is likely strongly driven by urbanization, and not biogeography. In sum, this thesis demonstrates that migration and genetic drift can rapidly impact the genetic variation in populations. In addition, I demonstrate that rare variant and haplotype based approaches are essential for examining the impact of migration and genetic drift between populations within an extremely recently founded region with minimal geographic barriers.