Y-chromosomal Aaron - Background

Background

Although membership in the Jewish community has, since at least the second century CE, been passed maternally (see: Who is a Jew?), tribal identity, and membership in the group that originally comprised the Jewish priesthood (Cohen or Kohen; plural: Cohanim or Kohanim), has been patrilineal. Modern Kohanim claim descent from a biblical person, Aaron, brother of Moses, in the direct lineage from Levi, the patriarch of the Tribe of Levi, great grandson of Abraham, according to the tradition codified in the Tanakh (שמות / Sh'mot/Exodus 6). DNA testing is aiding scholars to trace the lineages found among modern Jewish populations, including contemporary Cohen families, to decipher origins of the people groups who were joined to the ancient Israelites and to identify genetic admixture and genetic drift.

For human beings, the normal number of chromosomes is 46, of which 23 are inherited from each parent. Two chromosomes, the X chromosome and Y chromosome, determine sex. Women have two X chromosomes, one inherited from their mother, and one inherited from their father. Men have an X chromosome inherited from their mother, and the Y chromosome inherited from their father.

Males who share a common patrilineal ancestor also share a Y chromosome, diverging only with respect to accumulated mutations. Since Y-chromosomes are passed from father to son, all Kohanim men should theoretically have almost identical Y chromosomes; this can be tested with a genealogical DNA test. As the rate that mutations accumulate on the Y chromosome is relatively constant, scientists can estimate the elapsed time since two men had a common ancestor. (See molecular clock.) "The Samaritan M267 lineages differed from the classical Cohen modal haplotype at DYS391, carrying 11 rather than 10 repeats", as well as, have a completely different haplogroup, which should have been "J1". Samaritan Kohanim descend from a different patrilineal family line, having haplogroup E1b1b1a (M78) (formerly E3b1a).