Y-chromosomal Aaron - Genetic Studies

Genetic Studies

The Cohen hypothesis was first tested by Prof. Karl Skorecki and collaborators from Haifa, Israel, in 1997. In their study, "Y chromosomes of Jewish priests," published in the journal Nature, they found that the Kohanim appeared to share a different probability distribution compared to the rest of the Jewish population for the two Y-chromosome markers they tested (YAP and DYS19). They also found that the probabilities appeared to be shared by both Sephardic and Ashkenazi Cohens, pointing to a common Cohen population origin before the Jewish diaspora under the Roman empire. However, this study also indicated that only 48% of Ashkenazi Cohanim and 58% of Sephardic Cohanim have the J1 Cohen Modal Haplotype.

In a subsequent study the next year (Thomas MG et al., 1998), the team increased the number of Y-STR markers tested to six, as well as testing more SNP markers. Again, they found that a clear difference was observable between the Kohanim population and the general Jewish population, with many of the Cohen STR results clustered around a single pattern they named the Cohen Modal Haplotype:

	xDE	xDE,PR	Hg J	CMH.1	CMH		CMH.1/HgJ	CMH/HgJ
Ashkenazi Cohanim (AC):	98.5%	96%	87%	69%	45%		79%	52%
Sephardic Cohanim (SC):	100%	88%	75%	61%	56%		81%	75%
Ashkenazi Jews (AI):	82%	62%	37%	15%	13%		40%	35%
Sephardic Jews (SI):	85%	63%	37%	14%	10%		38%	27%

Here, becoming increasingly specific, xDE is the proportion who were not in Haplogroups D or E (from the original paper); xDE,PR is the proportion who were not in haplogroups D, E, P, Q or R; Hg J is the proportion who were in Haplogroup J (from the slightly larger panel studied by Behar et al. (2003)); CMH.1 means "within one marker of the CMH-6"; and CMH is the proportion with a 6/6 match. The final two columns show the conditional proportions for CMH.1 and CMH, given membership of Haplogroup J.

The data shows that the Kohanim were more than twice as likely to belong to Haplogroup J than the average non-Cohen Jew. Of those who did belong to Haplogroup J, the Kohanim were more than twice as likely to have an STR pattern close to the CMH-6, suggesting a much more recent common ancestry for most of them compared to an average non-Cohen Jew of Haplogroup J.

Further study published in 2009 found new markers and better defined variant J1e* (now J1c3, also called J-P58*). This research demonstrates that 46.1% of Kohanim carry Y chromosomes belonging to a single paternal lineage (J-P58*) that likely originated in the Near East well before the dispersal of Jewish groups in the Diaspora. Support for a Near Eastern origin of this lineage comes from its high frequency in our sample of Bedouins, Yemenis (67%), and Jordanians (55%) and its precipitous drop in frequency as one moves away from Saudi Arabia and the Near East (Fig. 4). Moreover, there is a striking contrast between the relatively high frequency of J-58* in Jewish populations (»20%) and Kohanim (»46%) and its vanishingly low frequency in our sample of non- Jewish populations that hosted Jewish diaspora communities outside of the Near East.

Thomas, et al. dated the origin of the shared DNA to approximately 3,000 years ago (with variance arising from different generation lengths). The techniques used to find Y-chromosomal Aaron were first popularized in relation to the search for the patrilineal ancestor of all contemporary living humans, Y-chromosomal Adam.