Tuesday, December 21, 2010

Ossetians

South Ossetian woman and boy (Link)

Map of the Caucasus Region

In the continuing investigation into candidate mtDNA and yDNA members of the ADMIXTURE K10 West Asian component, Ossetia is interesting in that its population has a high incidence of y haplogroups G and R1b (Myres et al).   Its mtDNA demonstrates continuity with surrounding Caucasus regions.  South Ossetia lies within the country of Georgia which is notable for its pronounced West Asian component which would suggest that both its mtDNA and yDNA distributions are correlated with the ADMIXTURE West Asian component.

An important 2004 paper examines the population composition of Ossetians and relates this to the linguistic and geographic structure in the region:

Genetic Evidence Concerning the Origins of South and North Ossetians
Nasidze, et al
(Link)

Summary: "Ossetians are a unique group in the Caucasus, in that they are the only ethnic group found on both the north and south slopes of the Caucasus, and moreover they speak an Indo-European language in contrast to their Caucasian-speaking neighbours. We analyzed mtDNA HV1 sequences, Y chromosome binary genetic markers, and Y chromosome short tandem repeat (Y-STR) variability in three North Ossetian groups and compared these data to published data for two additional North Ossetian groups and for South Ossetians. The mtDNA data suggest a common origin for North and South Ossetians, whereas the Y-haplogroup data indicate that North Ossetians are more similar to other North Caucasian groups, and South Ossetians are more similar to other South Caucasian groups, than to each other. Also, with respect to mtDNA, Ossetians are significantly more similar to Iranian groups than to Caucasian groups. We suggest that a common origin of Ossetians from Iran, followed by subsequent male-mediated migrations from their Caucasian neighbours, is the most likely explanation for these results. Thus, genetic studies of such complex and multiple migrations as the Ossetians can provide additional insights into the circumstances surrounding such migrations."

Y Chromosome STRs:  "Since haplogroup G(M201) has an unusually high frequency in North Ossetian (average frequency = 0.57) compared with other groups from the Caucasus (average frequency = 0.21), we typed 9 Y-STR loci in individuals with this Y-SNP haplogroup to determine if this elevated frequency indicates a bottleneck effect.We compared the results with the same set of loci on the same Y-SNP background typed in other groups from the Caucasus (Nasidze et al. 2003). Haplotype diversity(M201) is significantly reduced in Ossetians (0.722± 0.071) compared± 0.005). A median network of Y-STR haplotypes on the background∗(M201) revealed two clearly separated clusters (Figure 3). One of them almost exclusively contains haplotypes found in the Digora group. The second cluster contains the remaining North Ossetian groups, suggesting either different sources of introduction of haplogroup G∗(M201) or isolation and genetic drift in the Digora group."

Comparison of mtDNA and Y-Chromosome Data: "The geographic and linguistic structure of Ossetians, other Caucasus groups, and European, West and Central Asian groups, as assessed by mtDNA and Y chromosome variation, was investigated by the AMOVA procedure (Table 4). As is typically seen in human populations, the within-populations proportion of the variance was much higher for mtDNA (about 96% than for the Y chromosome (about 76-77%). For both the mtDNA and the Y-SNP data, the geographic classification of populations gave a slightly better fit to the genetic data (in terms of higher among-group variance and lower among-populations-within-groups variance) than did linguistic classifications (Table 4). Further classifying the Caucasian groups into South and North groups did not significantly improve the fit of either classification to the data (Table 4)."

Discussion:

"North and South Ossetians are the only ethnic group found on both slopes of the Caucasus Mountains. They speak a language which belongs to the Iranian branch of the Indo-European language family; hence, Ossetians are a linguistic isolate, surrounded by Caucasian speaking populations. By surveying mtDNA and Ychromosome variation in Ossetians, we sought answers to several questions concerning the origins and genetic relationships of Ossetians. First, are North and South Ossetians more genetically similar to each other, or to their geographic neighbours (i.e., Caucasian-speaking populations in the North and South Caucasus, respectively)? The results are somewhat different for mtDNA vs. the Y-chromosome. North and South Ossetians do cluster somewhat in the MDS plot based on mtDNA (Fig. 2A), which may indicate a common origin. However, for the Y-chromosome, North Ossetians are more similar to other North Caucasian populations, and South Ossetians to other South Caucasian populations, than to each other. The SAMOVA analysis also identifies a boundary between South Ossetians and other groups for the Y chromosome, but not for mtDNA. Thus, there is no indication in the Y-chromosome of a particularly close genetic relationship between N. Ossetians and S. Ossetians. If they did have a common origin in the past, it has apparently become obscured by subsequent gene flow with their geographic neighbours on the same sides of the Caucasus Mountains.

"Putting together the archaeological and genetic data, and assuming a common origin of South and North Ossetians (which is supported by the mtDNA data), a plausible scenario is that “alteration” of the initial Ossetian Y-chromosome gene pool took place in North Ossetians via other North Caucasus groups. This assumption is enforced by the fact that the genetic distances between North Ossetians and South Caucasus groups are similar to those between North Ossetians and South Ossetians, but the genetic distances between North Ossetians and other North Caucasus groups are much smaller. Moreover, there are differences in genetic structures based on Y chromosome and mtDNA, as the correlation between Fst distances among pairs of Caucasus groups based on mtDNA and Y-haplogroups was not statistically significant. The different patterns observed between South and North Ossetians for the Y chromosome may also have been reinforced by the traditional patrilocal social structure of this population, leading to a higher degree of differentiation for the Y chromosome than for mtDNA.

"The Ossetians speak an Iranian language; is this because they are directly descended from the Alani (an Iranian-speaking group), or is it rather that genetically the Ossetians resemble their geographic neighbours in the Caucasus, and hence replaced their ancestral Caucasian language with an Iranian language, after contact with the Alani (or another group)? Average pairwise Fst values are smaller between Ossetians and Iranians than between Ossetians and Caucasians for both mtDNA and the Y chromosome, significantly so for mtDNA, which suggests an Iranian origin of Ossetians. Subsequent and largely male-mediated migrations between Ossetians and neighbouring groups in the North and South Caucasus, respectively, would explain the greater similarity between Ossetians and Caucasians for the Ychromosome, as discussed previously.

"In conclusion, the genetic results are supported by the archaeological record, in that they reflect a common Iranian origin of South and North Ossetians, as well as a genetic footprint of ancient migrations in the North Caucasus that mostly involved male individuals. Thus, genetic studies of such complex and multiple migrations as the Ossetians can provide additional insights into the circumstances surrounding such migrations."