High Coverage Mitogenomes and Y-Chromosomal Typing Reveal Ancient Lineages in the Modern-day Székely Population in Romania

Here we present 115 whole mitogenomes and 92 Y-chromosomal STR and SNP profiles from a Hungarian ethnic group, the Székelys (in Romanian: Secuii, in German: Sekler) living in southeast Transylvania (Romania). The Székelys can be traced back to the 12th century in the region, and numerous scientific theories exist as to their origin. We carefully selected sample providers that had local ancestors inhabiting small villages in the area of Odorheiu Secuiesc/Székelyudvarhely in Romania. The results of our research and the reported data signify a qualitative leap compared to previous studies, since complete mitochondrial DNA sequences and Y-chromosomal data containing 23 STRs have not been available from the region until now. We evaluated the results with population genetic and phylogenetic methods, in the context of the modern and ancient populations that are either geographically or historically related to the Székelys. Our results demonstrate a predominantly local uniparental make-up of the population that also indicates limited admixture with neighbouring populations. Phylogenetic analyses confirmed the presumed eastern origin of certain maternal (A, C, D) and paternal (Q, R1a) lineages and, in some cases, they could also be linked to ancient DNA data from Migration Period (5th-9thcenturies AD) and Hungarian Conquest Period (10th century AD) populations.