The 'Cohen' Gene,Rabbi YAAKOV KLEIMAN

Dr. Karl Skorecki was attending synagogue services one morning. The Torah was removed from the ark and a Cohen was called up for the first aliyah. The Cohen summoned that particular morning was a visitor: a Sephardic Jew whose parents were from Morocco. Dr. Skorecki also has a tradition of being a Cohen, though of Ashkenazic background: His parents were born in Eastern Europe. He looked at the Sephardic Cohen's physical features and considered his own. They were significantly different in stature, skin coloration and hair and eye color.

A nephrologist and a top-level researcher at the University of Toronto and at the Rambam-Technion Medical Center in Haifa, Dr. Skorecki was involved in the breakthroughs in molecular genetics which are revolutionizing medicine and the study of the life-sciences. He was also aware of the newly developing application of DNA analysis to the study of history and population diversity.

Dr. Skorecki considered, "According to tradition, this Sephardi and I are both direct descendants of one man, Aaron the Cohen. Could this line have been maintained since Sinai and throughout the long exile of the Jewish people?"

As a scientist, he wondered, could such a claim be tested? He considered a hypothesis: If all Cohanim are descendants of one man, they should have a common set of genetic markers, a common haplotype ? that of their common ancestor. In this case, Aaron the Cohen.

Building The Hypothesis

A genetic marker is a variation in the nucleotide sequence of the DNA, known as a mutation. Mutations which occur within genes ? a part of the DNA which codes for a protein usually cause a malfunction or disease, and is lost due to selection in succeeding generations. However, mutations found in so-called "non-coding regions" of the DNA tend to persist.

Since the (male) Y chromosome consists almost entirely of non-coding DNA, it would tend to accumulate mutations. Since it is passed from father to son without recombination, the genetic information on a Y chromosome of a man living today is basically the same as that of his ancient male ancestors, except for the rare mutations that occur along the hereditary line. A combination of these neutral mutations, known as a haplotype, can serve as a genetic signature of a man's male ancestry. Maternal genealogies are also being studied by means of the m-DNA (mitrocondrial DNA), which is inherited only from the mother.

Dr. Skorecki then made contact with Professor Michael Hammer of the University of Arizona, a leading researcher in molecular genetics and a pioneer in Y chromosome research. Professor Hammer uses DNA analysis to study the history of populations, their origins and migrations. His previous research included work on the origins of the Native American Indians and the development of the Japanese people.

A study was undertaken to test the hypothesis. If there is a common ancestor, the Cohanim should have common genetic markers at a higher frequency than the general Jewish population.

Astonishing Results

In the first study, as reported in the prestigious British science journal, "Nature" (January 2, 1997), 188 Jewish males were asked to contribute some cheek cells from which their DNA was extracted for study. Participants from Israel, England and North America were asked to specify whether they were a Cohen, Levi or Israelite, and to identify their family background.

The results of the analysis of the Y chromosome markers of the Cohanim and non-Cohanim were indeed significant. A particular marker (YAP-), was detected in 98.5 percent of the Cohanim, and in a significantly lower percentage of non-Cohanim.

In a second study, Dr. Skorecki and associates gathered more DNA samples and expanded their selection of Y chromosome markers. Solidifying their hypothesis of the common ancestor of Cohanim, they found that a particular array of six chromosomal markers were found in 97 of the 106 Cohanim tested. This collection of markers has come to be known as the Cohen Modal Haplotype (CMH) ? the standard genetic signature of the Jewish priestly family. The chances of these findings happening at random is greater than one in 10,000.

The finding of a common set of genetic markers in both Ashkenazic and Sephardic Cohanim worldwide clearly indicates an origin pre-dating the separate development of the two communities around 1000 CE. Date calculation based on the variation of the mutations among Cohanim today yields a time frame of 106 generations from the ancestral founder of the line, some 3,300 years, the approximate time of the exodus from Egypt, the lifetime of Aaron the Cohen.

Tribal Descent

Professor Hammer was recently in Israel for the Jewish Genome Conference. He confirmed that his findings are consistent: over 80 percent of self-identified Cohanim have a common set of markers. The finding that less than one-third of the non-Cohen Jews who were tested possess these markers is not surprising to the geneticists. "Jewishness" is not defined genetically. Other Y chromosomes can enter the Jewish gene pool through conversion or through a non-Jewish father. Jewish status is determined by the mother. Tribe membership follows the father's family line.

Calculations based on the high rate of genetic similarity of today's Cohanim resulted in the highest "paternity-certainty" rate ever recorded in population genetics studies ? a scientific testimony to family faithfulness.

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. A common geographical origin can be seen for all mainstream Jewish groups studied.

This genetic research has clearly refuted the once-current libel that Ashkenazic Jews are not related to the ancient Hebrews, but are descendants of the Kuzar tribe ? a pre-10th century Turko-Asian empire which reportedly converted en masse to Judaism. Researchers compared the DNA signature of the Ashkenazic Jews against those of Turkish-
derived people, and found no correspondence.

Levite Numbers

In their second published paper in "Nature" (July 9,1998), the researchers included an unexpected finding.

Those Jews in the study who identified themselves as Levites did not show a common set of markers as did the Cohanim. The Levites clustered in three groupings, one of them the CMH. According to tradition, they should also show a genetic signature from a common patrilineal ancestor.

It is interesting to note that the tribe of Levi has a history of a lack of quantity. The census in the Biblical Book of Numbers shows Levi to be the smallest of the tribes. After the Babylonian exile, the Levites failed to return en masse to Jerusalem, though urged by Ezra the Scribe to do so. (They were therefore fined by losing their exclusive rights to tithes.) Though statistically, the Levites should be more numerous than Cohanim, in synagogues today it is not unusual to have a minyan with a surplus of Cohanim, yet not one Levi. Researchers are now focusing efforts on the study of the genetic make-up of Levites to learn more about their history in the Diaspora.

Using the CMH as a DNA signature of the ancient Hebrews, researchers are pursuing a hunt for Jewish genes around the world. The search for lost tribes, whether the Biblical Ten Lost Tribes which were uprooted from the land of Israel by the Assyrians, or other would-be Jews, Hebrews or "chosen peoples," is not new. Using the genetic markers of the Cohanim as a yardstick, these genetic archaeologists are using DNA research to discover historical links to the Jewish people.

Many individual Cohanim and others have approached the researchers to be tested. The researchers' policy is that the research is not a test of individuals, but an examination of the extended family. Having the CMH is not proof of one's being a Cohen. At present, there are no ramifications [in Jewish law] of this discovery. No one is certified nor disqualified because of his Y chromosome markers.

The research, which began with an idea in synagogue, has shown a clear genetic relationship amongst Cohanim and their direct lineage from a common ancestor. The research findings support the Torah statements that the line of Aaron will last throughout history...

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