In total, 495 DNA samples from different collections (
Table 1
) were screened for the Y chromosome polymorphism M17. The average frequency of the haplogroup R-M17 in Ashkenazi Jews (11.5%, 57 individuals) is significantly higher (
P
<0.05) than that in Sephardic Jews (3.9%), Kurdish Jews (4%) and Palestinian Arabs (1.4%). To date, comparable frequencies of R-M17 in other Middle Eastern populations have been reported in Moslem Kurds, Syrians and Lebanese (
Table 2
). However, the haplotype distribution within R-M17, available only for Moslem Kurds, is very different from that of Ashkenazim.
4
These data suggest that the increase in R-M17 in Ashkenazim occurred after they had gone into the Diaspora.
Variation within R-M17 was examined by analysing 56 of the 57 chromosomes for six microsatellite loci. Apart from one singleton (haplotype H9), the other 13 haplotypes form a compact network (
Figure 1
). The star-like pattern and the low level of diversity are indicative of a founder effect. The most common R-M17 haplotype in the total Ashkenazi sample (
∼
45%), haplotype 6 (H6), is most likely the ancestral haplotype of this haplogroup among Ashkenazim. The time to the most recent common ancestor of R-M17 in Ashkenazim
9
was estimated to 62.7 generations ago (excluding H9), using the previously published mutation rate for the six microsatellite loci studied here (
μ
=1.8 × 10
?3
with 95% CI 9.8 × 10
?4
?3.1 × 10
?3
).
10
Assuming a generation time of 25 years, this amounts to 1567 years ago (95% CI 2877?910 years ago).
If R-M17 had been present in substantial frequency in the pre-Diaspora Y chromosome pool, one would expect to observe the ancestral haplotype H6 in other Jewish groups and in Palestinians who share a large portion of their Y chromosomes with Jews.
3
,
4
,
11
However, in a combined non-Ashkenazi sample of 320 individuals (Sephardic, Kurdish Jews and Palestinians),
4
H6 was found only in a single Sephardic Jew (0.3%;
Figure 1
). This finding strongly suggests gene flow from an external population into the Ashkenazi gene pool.
Where did the R-M17 chromosomes in Ashkenazim come from? The haplogroup R-M17 has a wide geographic distribution in Europe, West Asia and the Middle East, with the highest frequencies in Eastern European populations (
Table 2
). Haplotype H6 is also present at considerable frequencies in various Eastern European populations,
5
,
12
,
13
but is absent or found only at very low frequencies in Central and West Asians and in Middle Easterners.
14
,
15
Thus, R-M17 in Ashkenazi Jews could represent gene flow from Eastern European populations. This scenario is supported by the lower haplotype diversity measures (
h
) in Ashkenazim (0.735±0.05) compared to those of Eastern European populations
5
(ranging from 0.894±0.022 to 0.919±0.026), and by the fact that in a combined Ashkenazi?European network, Jews present only a subset of the haplotypes (not shown).
The widespread distribution of R-M17 in Europe might suggest multiple gene flow events from the European host populations into Ashkenazim. However, we observed that the frequencies of R-M17 in Jews from various countries (Germany, Lithuania, Czechoslovakia, Hungary, Romania, Poland, Russia and the Ukraine) ranged from 12?13% in Russia and Ukraine to 22% in Germany and Lithuania, and did not differ from one another (
P
>0.05). Likewise, the haplotypes of Jews from these countries showed very similar distribution patterns in a network (not shown). Furthermore, the frequencies of R-M17 in different Ashkenazi communities did not correspond to the east?west cline seen in Europeans. Altogether, these results support the hypothesis of a single male founder who introduced R-M17 into the Ashkenazi gene pool at the beginning of the Jewish Diaspora in Europe. Since then this haplogroup has expanded and spread among the Jewish communities across Europe.
Noteworthy, Behar
et al
,
6
in their sample of Ashkenazi Levites, found R-M17 at a frequency of 52% and its modal haplotype (identical to H6 in the present study) at 74% within this haplogroup. They suggested a founder event specific to this particular group as a result of intrusion of one or a few European Y chromosomes into the forming Ashkenazi community. The present study does not necessarily contradict that of Behar
et al
,
6
but rather indicates that R-M17 is characteristic of the general Ashkenazi population and not restricted to the Levites. The proportion of Levites in different Jewish populations has been estimated to range from 0.25
16
to 3.4%.
17
Thus, their contribution to the overall frequency of R-M17 in Ashkenazim could not exceed 2%, while the frequency observed in the present study is 11.5%. Similar frequency (9.7%) was also reported by Passarino
et al
.
5
Furthermore, the haplotype diversity in the Ashkenazi Levites (0.451)
6
is lower than in the sample of Ashkenazi Jews described here, suggesting that R-M17 drifted to high frequency in the Levites more recently than in the general Ashkenazi population.
It is historically well documented that the Khazar King Bulan and his court converted to Judaism at the end of the 8th century CE.
1
The Khazars were originally a Turkic tribe from Central Asia who settled in the northern Caucasus and later spread to southern Russia and eastern Ukraine. Some authors argue that after the fall of their kingdom in the second half of the 10th century CE, the Khazar converts were absorbed by the emerging Ashkenazi Jewish community in Eastern Europe.
18
,
19
Since R-M17 haplogroup is also found at moderate to high frequencies in Central Asia
20
and southern Russia/Ukraine,
5
this haplogroup could have been present in the Khazars. However, if the R-M17 chromosomes in Ashkenazi Jews do indeed represent the vestiges of the mysterious Khazars then, according to our data, this contribution was limited to either a single founder or a few closely related men, and does not exceed
∼
12% of the present-day Ashkenazim.