Question: What is a Kohen?
Answer: Temple Priests
In the days of the Temple in Jerusalem, Kohanim (plural for Kohen) were priests responsible for worship ceremonies, such as leading services, offering sacrifices, burning incense and more. To maintain a high degree of purity, Kohanim observed certain prohibitions concerning marriage and contact with the deceased.
The High Priest
The High Priest, called HaKohen HaGadol, was the head of all the priests. He conducted services in the Temple on Yom Kippur, the holiest day of the Jewish year. And he was the only person allowed to enter the Holy of Holies, the holiest place in the Temple.
Today a Jew is considered a Kohen if he is a descendent of the first priest Aaron, the brother of Moses, from the Levi tribe.
In 1997, Dr. Karl Skorecki, a nephrologist and a top-level researcher at the University of Toronto and the Rambam-Technion Medical Center in Haifa, believed that if today's Kohanim are the descendants of one man (Aaron HaCohen), then they should have a common set of genetic markers at a higher frequency than the general Jewish population. Skorecki's study found that a particular marker (YAP-) was detected in 98.5 percent of the Kohanim, and in a significantly lower percentage of non-Kohanim. In addition, researchers found that a particular array of six chromosomal markers, called the Cohen Modal Hapoltype (CMH), was found in 97 of the 106 Kohenim tested. The chances of these findings happening at random is greater than one in 10,000. Thus, recent scientific research has proven a clear genetic relationship among Kohanim and their direct lineage from a common ancestor.
Today's Kohanim maintain a number of privileges and obligations within Jewish practice. They recite the Priestly Blessing during some worship services, and they are first to be called up (given an aliyah) to read from the Torah. Kohanim who follow Orthodox Judaism still observe prohibitions such as not marrying a divorced woman or a convert and not visiting a cemetery or coming into contact with the dead.