I read this very interesting article (JP) today and I would like to share it with you all, here it is:
The Book of Exodus specifies that the male descendants of Aaron, the brother of Moses, should constitute the Jewish priesthood - the kohanim - "for all time." Jewish tradition holds that the status of kohen has been faithfully passed from father to son for more than 3,300 years. In 1997 the world was amazed to learn that the old Bible story had found new and very persuasive scientific support.
Seemingly out of the blue, a group of genetics researchers announced that they had evidence to support that story. The group, led by Israeli researcher Dr. Karl Skorecki, himself a kohen, reported that the evidence was in the DNA of one of the 46 chromosomes that each kohen carries. Skorecki realized that Y chromosomes, which confer male sex, are passed down, just as the status of kohen is, from father to son. And like all chromosomes, the Y always displays a pattern of mutations called a "haplotype" that varies across family groups, and therefore can be used to trace descent. Thus, any haplotypes that were on Aaron's Y chromosome ought to appear with only minor changes in all of his descendants, including modern kohanim if they were in fact Aaron's offspring. In other words, kohanim should share a common genetic signature.
And so they do. A distinctive haplotype, now known as the "kohen modal haplotype," was found in 45 percent-61% of Ashkenazi kohanim, 56%-69% of Sephardi kohanim and 10%-15% of other male Jews. The haplotype is estimated to be between 2,100 and 3,250 years old, a time range that includes the biblical period.