The focus of my research is to better understand the factors that shape genetic variation. These can be divided into factors that shape the entire genome (e.g., demographic factors such as population expansion) and those that affect a single locus or small subset of loci (e.g., selection). My work employs an interdiciplanary approach to characterizing the forces that have affected genetic variation drawing upon the fields of population genetics, anthropology, epidemiology, molecular evolution and genomics.
The haploid portions of the genome are useful tools for understanding recent evolutionary history because they are non-recombining and are uniparentally inherited. A comparision of the paternally-inherited Y chromosome with the maternally-inherited mtDNA can provide clues to sex-specific demographic processes that have occurred in the evolutionary past (e.g. differential male versus female migration). This part of my work examines associations between human African Y chromosome and mtDNA genetic distances with language or geographic distances to examine the effects of recent Neolithic migrations. Additionally, I have been involved in studies that focus on X chromosome loci that examine the effects of selection and demography on shaping patterns of human African and non-African diversity.
The HbS and HbC alleles at the beta-globin locus confer resistance to malaria but are under different selective pressures. In the homozygous state, the HbS allele is responsible for sickle cell anemia but protects the heterozygous individual from malaria and is therefore subject to balancing selection. Individuals with one or both of the HbC allele are protected from malaria. Hence, the HbC allele is under positive directional selection. The majority of my dissertation work examines patterns of sequence variation and levels of linkage disequilibrum to characterize the signal of selection and to date the origin of the HbS and HbC malarial-resistance alleles.
