ABSTRACT
Perhaps the study which received most publicity was the one on the Cohanim (Jewish priests). Cohanim, according to the Jewish tradition, are direct descendants of the priestly class originating with Aaron, the brother of Moses, and whose functions centred on the Israelite Temple. After its destruction the institution of the priesthood survived until today with this priestly status transmitted generation after generation from father to son. It was surmised that if this tradition was correct all Jewish priests should demonstrate some genetic similarities on the Y chromosome. This hypothesis was developed independently by Karl Skorecki from the Haifa Technion in Israel and Neil Bradman from University College London. Both scientists decided to conduct a study of the Cohanim from different Jewish communities in order to see whether there were any differences in the frequency of Y chromosome haplotypes (combinations of polymorphisms, or DNA changes) between priests and lay Jews. The results, initially published in 1997 in Nature, showed that such differences existed and were observable in both Ashkenazi and Sephardi Jewish communities which was significant because it immediately established a date for the beginning of such differences before the great historic division of the Sephardi and Ashkenazi groups over a 1,000 years ago. Scientists identified haplotypes of 188 unrelated Y chromosomes from Israeli, North American and British Jews. Cohanim were identified on the basis of questioning. Geneticists constructed haplotypes using first the presence or absence of the Y Alu polymorphic (YAP) insert, which is considered to represent a unique evolutionary event dated between 29,000 and 340,000 years ago, second, a polymorphic GATA repeat microsatellite, DYS19, and third, typing a subset of samples for a non-Y chromosome CA-repeat polymorphism, D1S191.1 The difference in the frequency of YAP chromosomes among the priests compared to lay Jews was striking: only 1.5 per cent of Y chromosomes among the priests were YAP, in comparison to a frequency of 18.4 per cent among other Jews. At the same time, no significant difference
was found in the distribution of alleles for the non-Y chromosomes locus polymorphism D1S191. According to the article, these results confirm a distinct paternal genealogy for the Cohanim, as this haplotype distinction could be made between the Cohanim and the lay Jews within both Ashkenazi and Sephardi communities, which is consistent with the tradition of the early origin of priesthood (Hammer et al. 1997).
