Molecular insight into the genesis of ranked caste populations of western India based upon polymorphisms across non-recombinant and recombinant regions in genome

Abstract

Background

Large-scale trade and cultural contacts between coastal populations of western India and Western-Eurasians paved for extensive immigration and genesis of wide spectrum of admixed gene pool. To trace admixture and genesis of caste populations of western India, we have examined polymorphisms across non-recombining 20 Y-SNPs, 20 Y-STRs, 18 mtDNA diagnostic sites, HVS-1 plus HVS-2 regions; and recombining 15 highly polymorphic autosomal STRs in four predominant caste populations- upper-ranking Desasth-brahmin and Chitpavan-brahmin; a middle-ranking Kshtriya Maratha; and a lower-rank peasant Dhangar.

Results

The generated genomic data was compared with putative parental populations- Central Asians, West Asians and Europeans using AMOVA, PC plot, and admixture estimates. Overall, disparate uniparental ancestries, and l.1% GST value for biparental markers among four studied caste populations linked well with their exchequer demographic histories. Marathi-speaking ancient Desasth-brahmin shows substantial admixture from Central Asian males but Paleolithic maternal component support their Scytho-Dravidian origin. Chitpavanbrahmin demonstrates younger maternal component and substantial paternal gene flow from West Asia, thus giving credence to their recent Irano-Scythian ancestry from Mediterranean or Turkey, which correlated well with European-looking features of this caste. This also explains their untraceable ethno-history before 1000 years, brahminization event and later amalgamation by Maratha. The widespread Palaeolithic mtDNA haplogroups in Maratha and Dhangar highlight their shared Proto-Asian ancestries. Maratha males harboured Anatolianderived J2 lineage corroborating the blending of farming communities. Dhangar heterogeneity is ascribable to predominantly South-Asian males and West-Eurasian females.

Conclusions

The genomic data-sets of this study provide ample genomic evidences of diverse origins of four ranked castes and synchronization of caste stratification with asymmetrical gene flows from Indo-European migration during Upper Paleolithic, Neolithic, and later dates. However, subsequent gene flows among these castes living in geographical proximity, have diminished significant genetic differentiation as indicated by AMOVA and structure.

Additional data files

Additional data files 1 and 2.