page_title: Genetic studies on Bulgarians
section_title: auDNA and overall
hierarchical_section_title: Genetic studies on Bulgarians / auDNA and overall
caption_attribution_description: English: Genetic structure of the Balto-Slavic populations within a European context according to the three genetic systems. a) PC1vsPC3 plot based on autosomal SNPs (PC1 = 0.53; PC3 = 0.26); b) MDS based on NRY data (stress = 0.13); c) MDS based on mtDNA data (stress = 0.20). We focus on PC1vsPC3 because PC2 (S1 Fig) whilst differentiating the Volga region populations from the rest of Europeans had a low efficiency in detecting differences among the Balto-Slavic populations–the primary focus of this work. doi:10.1371/journal.pone.0135820.g002
context_page_description: The Bulgarians are part of the Slavic ethnolinguistic group as a result of migrations of Slavic tribes to the region since the 6th century AD and the subsequent linguistic assimilation of other populations.
  Hellenthal et al, 2014 estimated from data of 94 modern populations a couple of analyses on Bulgarians inferred from an admixture event in 1000-1600 YBP between a Slavic and a Cypriot donor group: to a Polish donor group Bulgarians are of an estimated 59% Polish-like and 41% Cypriot-like admixture; to a Belarusian, Bulgarians are of 46% Belorussian-like and 54% Cypriot-like admixture. Early gene flows between southeastern and eastern Europe make it difficult to obtain a correct estimate, although young enough identical by descent segments confirmed such connection and that the East and West Slavs share more identical by descent segments with South Slavs than with Greeks, inter-Slavic populations, but less with Balts, while the South Slavs share similar number with East and West Slavs, but fewer with Greeks.
context_section_description: Whilst haploid markers such as mtDNA and Y-DNA can provide clues about past population history, they only represent a single genetic locus, compared to hundreds of thousands present in nuclear, autosomes. Although autosomal analyses often sample a small number of Bulgarians, by multiple autosomes multiple ancestral lines may be traced by an individual's 21 autosomes as opposed to one identical mtDNA or Y-DNA sex chromosome, whose inheritance although clinal, demonstrates genetic drift often in statistics. Analyses of autosomal DNA markers gives the best approximation of overall 'relatedness' between populations, presenting a less skewed genetic picture compared to Y-DNA haplogroups. This auDNA data shows that there are no sharp discontinuities or clusters within the European population. Rather there exists a genetic gradient, running mostly in a southeast to northwest direction. A study compared all Slavic nations and combined all lines of evidence, autosomal, maternal and paternal, including more than 6000 people for and at least 700 Bulgarians from previous studies, of which 13 were used for autosomal analysis (right image). The overall data situates the southeastern group (Bulgarians and Macedonians) in a cluster with Romanians, and they are at similar proximity to Gagauzes, Montenegrins and Serbs who are not part of another cluster but are described as 'in between' clusters. Macedonians and Romanians consistently appear to be among the most related to Bulgarians by au, mt, and Y-DNA a conclusion backed also by a pan-European autosomal study investigating 500,568 SNP (loci) of 1,387 Europeans and including 1 or 2 Bulgarians, other more or less extensive data sets situate Bulgarians and Romanians as their nearest . Per HLA-DRB1 allele frequencies Bulgarians are also in a cluster with the same populations. The Balto-Slavic study itself calculated genetic distance by SNP data of the multiple autosomes and ranked most proximal to Bulgarians the Serbs, followed by Macedonians, Montenegrins, Romanians, Gagauzes, Macedonian Greeks apart from Thessaloniki, the rest of the South Slavs, Hungarians, Slovaks, Czechs, and then by Greeks from Thessaloniki, Central Greece and Peloponnese. The East Slavs and Poles cluster together remaining less proximal to Bulgarians than Germans, among whom Slav admixture is also observed. Balts, however, according to the PCA analysis are less proximal to Bulgarians than Italians for example are. Bulgarians are also only modestly close to their eastern neighbours – the Anatolian Turks, suggesting the presence of certain geographic and cultural barriers between them. Despite various invasions of Altaic-speaking peoples in Europe, no significant impact from such Asian descent is recorded throughout southern and central Europe.
  The study claims that the major part of the Balto-Slavic genetic variation can be primarily attributed to the assimilation of the pre-existing regional genetic components, which differed for present West, East and South Slavic-speaking people. For Slavic peoples correlations with linguistics came out much lower than high correlations with geography. The South Slavic group, despite sharing a common language, is separated and has a largely different genetic past from their northern linguistic relatives. Therefore, for the Bulgarians and most other South Slavs the most plausible explanation would be that their most sizable genetic components were inherited from indigenous Balkan pre-Slavic and pre-Bulgar population. The South Slavs are characterized by featuring NRY hgs I2a and E plus 10% higher Mediterranean k2 autosomal component, while the Eastern and Western Slavs are characterized by the k3 component and hg R1a. The presence of two distinct genetic substrata in the genes of East-West and South Slavs would conclude that assimilation of indigenous populations by bearers of Slavic languages was a major mechanism of the spread of Slavic languages to the Balkan Peninsula.
  Southeastern Europeans share large numbers of common ancestors that date roughly to the times of the Slavic ex
caption: Balto-Slavic comparison by A (autosomal DNA), B (Y-DNA) and C (mtDNA plot).
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