Mapping variation in Duffy blood group by local environmental factors in northwestern and central Kenya

Abstract

The Duffy negative genotype confers protection from P. vivax malaria by inhibiting expression of DARC, the receptor by which P. vivax invades erythrocytes. Positive selection for the Duffy negative phenotype has caused high frequencies of the Duffy negative allele in sub-Saharan Africa, but allelic variation between local populations requires further investigation. In this study, I mapped allelic variation of 220 individuals from 32 locations in northwestern and central Kenya by temperature, precipitation, and altitude to understand if differences in local environments drive selection at the Duffy locus. Using temperature, precipitation, and elevation as environmental proxies for malaria transmission, I hypothesized that selection for the Duffy negative phenotype will be greatest in areas most suitable for malaria transmission on a regional scale. PCR and gel analysis of 861 samples showed significantly higher malaria infections in northern Kenya, however this region did not show a higher frequency of the Duffy negative allele despite increased malaria transmission. My results show little variation in allele frequencies between locations, suggesting that regional environmental factors do not drive selection at this locus. Instead, the Duffy negative allele appears to be evenly distributed across populations in northwestern and central Kenya. With the increasing urbanization of central Kenya and migration of individuals to urban centers, I suspect that this observed genetic similarity between regions can likely be explained by migration and population admixture. Further studies should test this hypothesis to better understand how changing environmental conditions—including migration and urbanization—shape selection for the Duffy allele.