Distribution of East Eurasian Y-Chromosome and Mitochondrial DNA Haplogroups across Eurasia: Insights into the Genetic Ancestry of Bulgarians

Abstract

The modern Bulgarian mitochondrial DNA (mtDNA) and Y-chromosome gene pools predominantly consist of Western Eurasian haplogroups. In contrast, the Eastern Eurasian lineages are found at very low frequencies in Bulgarians, being represented only by mtDNA haplogroups C (0.2%), D (0.4%) and Z (0.1%) (Karachanak et al., 2012) and Y-chromosome haplogroups C, N and Q (each 0.5%) (Karachanak et al., 2013). A similar pattern is observed in ancient mtDNA samples of proto-Bulgarian human remains, which belong exclusively to Western Eurasian mtDNA haplogroups (Nesheva et al., 2015). In order to investigate Bulgarian ancestry from the perspective of Eastern Eurasian haplogroups, we have analyzed the distribution of Y-chromosome haplogroups C, N and Q and mtDNA haplogroups C, D and Z across Eurasia. The survey was performed using literature data for more than 15,000 individuals from different Eurasian (sub-) populations for each of these haplogroups. The collected data were used to construct Eurasian frequency maps of the considered haplogroups and to test the significance of their incidence between Bulgarians and Europeans, European neighboring populations of Bulgaria and populations, which according to some historical conceptions could have common ancestry with proto-Bulgarians, namely: Altaian, Caucasus, Siberian and Central Asian populations. The spatial distribution of mtDNA haplogroups C, D and Z and Y-chromosome haplogroups C, N and Q contrasts their high frequency among Altaic populations and their occasional appearance in Bulgarians. Furthermore, the comparison of the occurrence of these haplogroups shows no link between Bulgarians and Altaic and Caucasus populations. Based on the substantial genetic input of proto-Bulgarians to the modern Bulgarian gene pool, the present study confirms the nonexistence of a close Y-chromosomal or mtDNA link between proto-Bulgarians on the one hand and Altaic and Caucasus populations on the other.