A genetic analysis shows that all of the Ashkenazi Jews alive today — of which there are more than 10 million — can trace their roots to a group of just 330 people who lived 600 to 800 years ago.

The new study, which now appears in the journal Nature Communications, involved the genetic analysis of 128 healthy Ashkenazi Jews. These complete genomes were in turn compared to each other, along with the DNA of 26 Flemish people from Belgium.

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Writing in the LA Times, Karen Kaplan explains more:

"Ashkenaz" in Hebrew refers to Germany, and Ashkenazi Jews are those who originated in Eastern Europe. (Sephardic Jews, by contrast, are from the areas around the Mediterranean Sea, including Portugal, Spain, the Middle East and Northern Africa.) About 80% of modern Jews have Ashkenazi ancestry, according to the Hebrew University of Jerusalem. Albert Einstein was an Ashkenazi Jew, as were Gertrude Stein and Carl Sagan. Steven Spielberg and Scarlett Johansson are also Ashkenazi Jews, along with three current members of the U.S. Supreme Court (Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan).

Despite their close ties with Europe, no more than half of their DNA comes from ancient Europeans, the researchers found. Only 46% to 50% of the DNA in the 128 samples originated with the group of people who were also the ancestors of the Flemish people in the study. Those ancient people split off from the ancestors of today's Middle Easterners more than 20,000 years ago, with a founding group of about 3,500 to 3,900 people, according to the study.

The rest of the Ashkenazi genome comes from the Middle East, the researchers reported. This founding group "fused" with the European founding group to create a population of 250 to 420 individuals. These people lived 25 to 32 generations ago, and their descendants grew at a rate of 16% to 53% per generation, the researchers calculated.

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As Kaplan notes in her article, scientists are interested in studying this group because it is genetically isolated; Jews historically marry within their faith, so this gene pool is relatively tight.

"That makes it easier to identify genes linked to specific diseases, like Parkinson's and cancer, links that could well apply to non-Jews as well," she writes.

Read the entire scientific study.

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