January 24, 2005

Y-STRs in Europe

A very important new paper uses short tandem repeat (STR) markers on the human Y-chromosome over a set of 12,700 European individuals. STRs are fast mutating, making them unsuitable for the inference of phylogeny, but conversely suitable for detecting more recent population movements.

The main finding of this study is the detection of a strong differentiation between an "eastern" and a "western" cluster of haplotypes. In Central Europe where these two clusters meet, the gradient of change is sharper on an east-west axis than on a north-south axis. These two main population groupings are placed in boxes in the following dendrogram.

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In the next figure, the first three dimensions of an MDS on ΦST is shown:

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Inspection of Fig. 1 suggests that the similarity of Y-STR haplotypes decays much more rapidly along an east-west than a north-south gradient, at least in central Europe. This notion was formally corroborated by a MDS analysis of all pair-wise FST values. The first dimension, accounting for almost 89% of the variance (Table 1), clearly shows a decomposition of the European Y-STR genetic structure into three major components (Fig. 4a), closely corresponding to the "Western", "Central" and "Eastern" sub-clusters of Fig. 2. The first dimension also highlights the genetic peculiarity of metropolitan Paris and Vienna, Finland, and the two Balkan-Slavic samples of Slovenia and Croatia in relation to their respective surroundings. The degree of east-west stratification of the European Y-STR haplotype spectrum was quantified by Spearman rank correlation analysis between the latitudinal and longitudinal distances, respectively, and pair-wise PHgrST (Fig. 5). For 81 samples, the correlation was stronger with longitude than with latitude, and the few populations showing a notably reversed effect were from the fringe of the continent (Fig. 5). Furthermore, whilst only five samples showed a negative correlation with longitude, namely Emilia Romagna (I), Vaesterbotten (S), Finland, Estonia and Northern Norway, the same was true for 12 samples with latitude. The second dimension of the MDS analysis revealed more subtle structural features, such as, for example, the distinction between the Turkish and non-Turkish samples in "Southern Europe" and the divide between the two Dutch meta-samples. The third dimension eventually depicted an underlying north-south gradient that is usually seen in Y-SNP studies of European populations (Rosser et al. 2000; Semino et al. 2000). However, since the second and third dimensions of the Y-STR MDS accounted for less than 10% of the variance (Table 1), the major geographic structuring associated with the two types of markers must be substantially different.

Now, with respects to the Greeks, the following observations can be made. Greeks belong to a cluster (see dendrogram above) which stretches from parts of Italy and Sicily to the west to Turkey and from Hungary in the north to Greece in the south. This area corresponds quite closely to that of Gimbutas' Old Europe and the Eastern Roman ("Byzantine") Empire. I am also reminded of what I wrote about 1.5 years ago:
The Aegean-Mediterranean racial element does not seem to have penetrated much to the north of Hungary along the continental route. Interestingly, Hungarians appear to have a significant frequency of Y chromosome haplogroup E -which has a peri-Mediterranean distribution- and were found to be more similar to Greeks than the Greeks' more immediate northern neighbors according to Cavalli-Sforza.
It is also interesting that the Balkan Slavs are not allied with the "Eastern European" cluster. This may indicate a limited extent of Proto-Slavic intrusion across the Danube, or the well-known Finno-Ugrian admixture in Eastern Slavs, or both.

In Table 2, the authors perform a pseudo-admixture analysis of the studied populations into Western, Eastern, and Other clusters. It is noteworthy that Greeks have 44% of the Western and 27% of the Eastern cluster. By contrast, Bulgarians have 53% of the Eastern cluster and 28% of the Western one, and Romanians 57/24% respectively, and Albanians 53/34%. Hence, it seems that Greeks are differentiated from their Balkan neighbors in being less "Eastern". In fact the fraction of the Eastern cluster in Greeks is similar to that in West Italians (20%) and Sicilians (18%). This underscores the limited influence of demographic processes taking part north of Greece on the Greek population.

The differentiation of Turks from Turkey and the Balkans from other Balkan populations on the second dimension of the MDS plot most likely indicates the presence of unique Anatolian or Central Asian haplotypes among the former, as the Turks were formed by an amalgamation of West Asian Caucasoids with Central Asians of mixed Caucasoid-Mongoloid background.

There is much more interesting information in the paper, e.g., "The area covered by the former German Democratic Republic significantly overlaps with the homeland of Slavic (i.e. Wendish) people from the Middle Ages, including the Sorbes, Pomeranes, Wagriens, Obodrites, and Ranes. This geographical coincidence would explain the obvious preservation of "Slavic" haplotypes in eastern Germany far better than, for example, the settlement of eastern European World War II refugees, since the latter were mostly Germans anyway." which confirms a recent study which arrived at the same conclusions.

Human Genetics (Published Online)

Signature of recent historical events in the European Y-chromosomal STR haplotype distribution

Lutz Roewer et al.

Abstract Previous studies of human Y-chromosomal single-nucleotide polymorphisms (Y-SNPs) established a link between the extant Y-SNP haplogroup distribution and the prehistoric demography of Europe. By contrast, our analysis of seven rapidly evolving Y-chromosomal short tandem repeat loci (Y-STRs) in over 12,700 samples from 91 different locations in Europe reveals a signature of more recent historic events, not previously detected by other genetic markers. Cluster analysis based upon molecular variance yields two clearly identifiable sub-clusters of Western and Eastern European Y-STR haplotypes, and a diverse transition zone in central Europe, where haplotype spectra change more rapidly with longitude than with latitude. This and other observed patterns of Y-STR similarity may plausibly be related to particular historical incidents, including, for example, the expansion of the Franconian and Ottoman Empires. We conclude that Y-STRs may be capable of resolving male genealogies to an unparalleled degree and could therefore provide a useful means to study local population structure and recent demographic history.


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