A survey of haplotype frequencies and linkage disequilibrium at the DRD2 locus in the Nilgiri hill tribes, South India

Abstract

DNA analysis has made it easier to study haplotypes, arrays of alleles at closely linked loci along the chromosome. These regions are short enough to show little or no recombination, and behave as blocks that might have ancient origins. Scoring these markers as haplotypes, allows analysis both in terms of haplotype frequencies and identity in terms of linkage disequilibrium. The human dopaminergic system is an important focus of study in the fields of neuropsychiatry and pharmacology; it is also a promising nuclear DNA marker in studies of human genome diversity. Haplotype frequencies and linkage disequilibrium for the dopamine D2 receptor gene (DRD2) was determined in 250 unrelated individuals from five tribal populations. The three marker systems in this study are highly polymorphic in all the five tribal populations and the haplotype system showed high level of heterozygosities. Out of the possible eight haplotypes, four are commonly shared by all the populations. The ancestral allele B2D2A1 accounts for 0.021 to 0.080, which was present in all the groups consistently. The linkage disequilibrium was statistically significant in all the populations. Data obtained in this study on DRD2 represent one of the small, but growing number of data sets examining disequilibrium and haplotype frequencies in human populations.