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January 26, 2004

Concurrent evidence

A reader sent me a link to this article which concludes: "This contrasting pattern of diversity in Ashkenazi populations is evidence for a reduction in male effective population size, possibly resulting from a series of founder events and high rates of endogamy within Europe." Fine and dandy, but I just keep recalling this article in Discover from 1995 which made many simlar points, it pointed out that the majority of Hungarian Jews in any given generation were paupers, and that wealthy mercentile and rabbinical families were the ones that had high fertility rates and perpetuated the Jewish people (through historical research of records). In other words, a small effective population size....

Excerpt below....

Update: Henry cautions me about relying on one locus (the Y chromosome). I guess I will make my assumption explicit for readers-when I post links to papers like this, I don't expect them to be definitive, rather, over the years, the multitude of studies will form a composite understanding of the history of various parts of the genome (especially nonrecombining regions like the Y & mtDNA obviously). The current methods of historical genetics just keep getting better, when I was in college I remember reading papers that talked about the problems with distinguishing between the Irish and Norwegians, as the noise overwhelmed the ability to distinguish the two groups statistically. This isn't true anymore it seems. Those who have ideological axes to grind will cherry pick from the studies to "prove" their points, that's not my intention, rather, each study is just another data point in a portrait that is only beginning to be clear.

Admixture estimates
Table 6 shows the haplogroups with the highest frequency differentials between European non-Jewish and non-Ashkenazi Jewish (Hammer et al. 2000) parental populations (see above) and a summary of the admixture estimates for AJ populations. Among the western AJ populations, haplogroups J-12f2b* and R-P25 were the most diagnostic for distinguishing the parental Jewish (P1) and the parental western NJ European population (P2W) components. Among the eastern AJ populations, haplogroups J-12f2b* and R-M17 were the most diagnostic for distinguishing the parental Jewish (P1) and the parental eastern NJ European population (P2E) components. All other haplogroups had values below 20% (data not shown). When these diagnostic haplogroups were used for analysis, the m y value was 8.1%11.4%, suggesting an even smaller contribution of European Y chromosomes to the Ashkenazi paternal gene pool than in the previous study by Hammer et al. (2000). Because of the apparently high level of admixture in Dutch Jews (m y value of 46.0%18.3%), we repeated the admixture calculation excluding the Dutch sample and found a lower estimate of admixture (~5%). Although not statistically significant, there was a higher level of admixture in eastern AJ versus western AJ populations. This is similar to differences in the levels of mtDNA introgression observed in western and eastern AJ populations (Behar et al. 2004).

[. . .]

This survey of variation at 32 binary (SNP) and 10 STR markers in a sample of 442 Ashkenazi males from 10 different western and eastern Europe communities represents the largest study of Ashkenazi paternal genetic variation to date. In a previous study by Hammer et al. (2000), a set of 18 SNPs was typed in a diverse Jewish sample that included 113 Ashkenazim from the US (the European provenance of these samples was unknown). This AJ sample was characterized by nine haplogroups that were also found in several other Jewish populations. Similarly, studies by Nebel et al. (2001) and Thomas et al. (2002) have included a modest Ashkenazi sample (i.e., <80 Y chromosomes) typed with a small set of SNPs (i.e., 13 and 10, respectively), and a set of six Y-STRs. The results of all three of these earlier surveys concur that Ashkenazi Jews (1) have been relatively isolated from host European non-Jewish populations, and (2) are closely related to non-Ashkenazi Jewish communities and some non-Jewish populations from the Near East. The phylogenetic resolution of these earlier studies was partly limited by the relatively small number of markers typed. For example, the identification of additional highly informative sublineages within the two most frequent Ashkenazi clades (E and J) was not possible because many recently discovered downstream markers were not available. The recent publication of highly congruent human Y-chromosome trees (Hammer et al. 2001; Underhill et al. 2001) and a standardized nomenclatural system for the resulting binary polymorphism-based consensus tree (YCC 2002) has provided an opportunity to understand paternal population origins, relationships, and dispersals with more phylogenetic and geographic resolution than was heretofore possible. Analyses of the higher resolution dataset presented here provide a better opportunity to infer the composition of the founding Ashkenazi paternal gene pool and to distinguish lineages that may have entered the Ashkenazi population after their arrival in Europe.

Origins of Ashkenazi NRY lineages
Based on the frequency and distribution of the 20 haplogroups observed in AJ and NJ populations, we subdivided Ashkenazi Jewish lineages into the following three categories: major founder haplogroups, minor founder haplogroups, and shared haplogroups. The first two categories include those haplogroups likely to be present in the founding Ashkenazi population (and that now occur at high and low frequency, respectively). The latter category is comprised of haplogroups that either entered the Jewish gene pool recently as the result of introgression from European host populations, and/or that were present in both European and Jewish populations before the dispersal of ancestral Ashkenazim into Europe. We acknowledge that such categorization is complicated because current haplogroup distributions are the culmination of many past events. For example, haplogroups such as R-M17 and R-P25 that predominate in European populations today (see below) may have also been present in the Near East as part of the ancestral AJ gene pool. Similarly, haplogroups that predominate in AJ may have entered the European gene pool before AJ populations dispersed into Europe.

Paragroup EM35* and haplogroup J-12f2a* fit the criteria for major AJ founding lineages because they are widespread both in AJ populations and in Near Eastern populations, and occur at much lower frequencies in European non-Jewish populations. Because they have similar distributions as these major founder lineages, albeit at lower frequencies, we suggest that haplogroups G-M201 and Q-P36 are minor AJ founding lineages. Although J-M172 is also found at high frequency in AJ populations (and probably migrated to Europe with the original founding Ashkenazi population), its presence in European non-Jews at a frequency of 6% may reflect a more complicated history of migration to Europe (i.e., both before and during the Jewish Diaspora). This migration may have been mediated either by the diffusion of Neolithic farmers from the Near East between 4,000 and 7,500 years ago (Semino et al. 2000) or by sea-faring peoples in the Mediterranean region (Mitchell and Hammer 1996). Interestingly, M35+ chromosomes (E3b*; or their evolutionary precursors E* and E3*) were previously hypothesized to have migrated to Europe with farmers in the Neolithic (Hammer et al. 1997; Rosser et al. 2000; Semino et al. 2000). However, because M35* chromosomes are rare in Europe, we instead hypothesize that the derived lineage, E-M78 (E3b1), is the more likely haplogroup reflecting Neolithic demic diffusion. Similarly, we suggest that G-P15 with its better representation in Europe, rather than its evolutionary precursor G-M201 (which is found mainly in AJ populations), is a better candidate marker for Neolithic migrations of farmers into Europe.

The best candidates for haplogroups that entered the AJ population recently via admixture include I-P19, R-P25, and R-M17. These haplogroups are thought to represent the major Paleolithic component of the European paternal gene pool, expanding from refugia populations after the Last Glacial Maximum more than 10,000 years ago (Rosser et al. 2000; Semino et al. 2000). Because haplogroups R-M17 and R-P25 are present in non-Ashkenazi Jewish populations (e.g., at 4% and 10%, respectively) and in non-Jewish Near Eastern populations (e.g., at 7% and 11%, respectively; Hammer et al. 2000; Nebel et al. 2001), it is likely that they were also present at low frequency in the AJ founding population. The admixture analysis shown in Table 6 suggests that 5%-8% of the Ashkenazi gene pool is, indeed, comprised of Y chromosomes that may have introgressed from non-Jewish European populations. In particular, the Dutch AJ population appears to have experienced relatively high levels of European non-Jewish admixture. This is apparent in the MDS plot and by virtue of their elevated frequencies of haplogroups R-P25 (>25%) and I-P19 (>10%). These results are not surprising in view of the longstanding religious tolerance in this region. However, Dutch Jews do not appear to have increased levels of European mtDNA introgression (Behar et al. 2004), suggesting that admixture in this population is mainly the result of higher rates of intermarriage between Jewish woman and non-Jewish men.

Posted by razib at 10:42 PM