Cohanim (plural of Cohen) are the priestly family of the Jewish people, members of the Tribe of Levi.
The books of Exodus and Leviticus describe the responsibilities of the Cohanim, which include the Temple service and blessing of the people.
The Cohen line is patrilineal -- passed from father to son without interruption for 3,300 years, or more than 100 generations. Skorecki considered, "According to tradition, this Sephardi Cohen and I have a common ancestor.
Could this line have been maintained since Sinai, and throughout the long exile of the Jewish people?
The finding that less than one-third of the non-Cohen Jews who were tested possess these markers is not surprising to the geneticists. Other Y-chromosomes can enter the Jewish gene pool through conversion or through a non-Jewish father. Even a low rate of infidelity would have dramatically lowered the percentage." [Science News, October 3, 1998] Wider genetic studies of diverse present day Jewish communities show a remarkable genetic cohesiveness.
Jews from Iran, Iraq, Yemen, North Africa and European Ashkenazim all cluster together with other Semitic groups, with their origin in the Middle East.
This collection of markers has come to be known as the Cohen Modal Hapoltype (CMH) -- the standard genetic signature of the Jewish priestly family.