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founder effect in ashkenzi jewish people

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  • founder effect in ashkenzi jewish people

    I was talking to a friend about the founder effects that seem to have been found in ashkenezi people in both mtDNA and YDNA (tho I believe not everyone agrees). But the question I couldn't answer - don't really remember - is how small did the askenezi population get in eastern europe before it had the massive population explosion? does anyone remember the number?

  • #2
    The mtdna Behar paper cites some papers saying that the Ashkenazi population was about 25,000 in the 12th and 13th centuries, but the bottlenecks were before that. He cites a paper talking abuot the "establishment of the Ashkenazi population during the 7th and 8th centuries in the Rhine valley by a few migrating families arriving from Northern Italy" (Ostrer 2001, A genetic profile of contemporary jewish populations. Nat Rev. Genet. 2:891-898).

    cacio

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    • #3
      thanks cacio - i had read the behar paper, but not the Ostrer paper. the numbers are helpful. didn't realize it was so few people - only "a few" families going to rhine valley - though I guess "a few" can mean different things to different people. I suppose i'll need to reread to remind myself also of when the bottleneck was and if there was more than one.
      Last edited by penguin; 13 September 2008, 02:34 PM.

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      • #4
        Note that there are no consensus estimates for the size of the Jewish population. Looking at rare genetic diseases is only one strategy. For example, Prof. Sergio Della Pergola of Hebrew University suggested a Middle Ages population of one million Jews worldwide based on very limited historical records.

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        • #5
          I lean toward the lower figure, but any dna based estimate must take into account the destructive impact of the Holocaust, forced conversion of Jews from the Dark Ages onward as well as well as emigration. For example, there may be genetic differences between 19th century Ashkenazim and 21th century Ashkenazim due to the non-uniform effects of the Holocaust and emigration from Europe. How can one generalize from studies in the 21th century. In other words, there will be an inevitable gap between data and conclusion and any estimate will be based on somewhat debatable assumptions.

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          • #6
            I suppose that the della Pergola number is about total Jews, Sephardi and Ashkenazi. During the middle ages, I would assume that the vast majority of Jews lived in the muslim world (North Africa, Spain, Levant), an area that was more heavily populated than Europe. The 1m number then does not seem unreasonable. But for the Ashkenazi, the number must have been much much lower, the 25,000 seems more to the point, though it probably implies a rate of population growth greater than for the rest of Europe since then.

            cacio

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            • #7
              Yes, I lean toward the lower estimate, but am concerned about the methodology upon which the estimates are based. For example, did the estimates consider the great inter-national variation in the "Jewish" K1a subclades of Ashkenazim women, i.e. such studies usually contain biased rather than representative samples. Did the estimates only look at Jews or did the studies include the large number of converted descendants of Middle Ages Jews --this could lead to a serious underestimation of the Jewish population. Etc.

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              • #8
                P.S. The reference to the inter-national differences in K1 among Ashkenazi women is: J. Feder --European Journal of Human Genetics (2008 I think). Her team found a K1 rate of 17% among Russian Jews but a K1 rate of 38% (more than double) among Polish Jews. I expect that this would lead to significant differences in founder effect estimates.

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                • #9
                  I think the founder population of 25,000 Jews in Germany was based upon historical research: http://hugr.huji.ac.il/AshkenaziJews.aspx

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                  • #10
                    All the references on the website are genetic rather than historical. It is not clear as to how they arrived at the estimate of 20,000. My main point is that both historical and genetic estimates are based on questionable assumptions and a limited amount of available data.

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                    • #11
                      Yes, but the very small Jewish population in Eastern Europe prior to 1600 is well-documented.

                      One study from the Jewish Agency: (estimates):
                      http://www.jewishagency.org/JewishAg...modern+age.htm

                      Jewish Populations: Jewish Encyclopedia
                      http://www.jewishencyclopedia.com/ta...le=STATISTICS:

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                      • #12
                        Neil Risch:
                        http://www.pubmedcentral.nih.gov/art...?artid=1180346

                        "The Founder Effect Theory

                        Stanford University geneticist Neil Risch explains the range of genetic diseases unique to the Ashkenazi Jewish population by theorizing that most of today's Ashkenazi Jews descend from a group of perhaps only a few thousand people - the more privileged Ashkenazi that lived 500 years ago in Eastern Europe.

                        The poorer Ashkenazi Jews, says Risch, had fewer children that lived to adulthood and, as a result, did not pass on as many genetic conditions. Geneticists refer to this relatively small group of ancestors as founders.

                        Until recently, both religious and political factors helped to ensure that Ashkenazi Jews married other Ashkenazi Jews. Today, millions of people may be able to trace their ancestry directly to these founders. Thus, even if just a few founders had a mutation, the gene defect would become amplified in the population. "

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                        • #13
                          I had these references in mind when I indicated my reluctance to accept such specific estimates. (I have already listed a few problems with founder effect studies---historical estimates also have problems e.g. converts were not included in counts ).

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                          • #14
                            I found a promising reference (though clearly historical population projections will always be estimates, since there were few good censuses in the past)

                            http://www.amazon.com/Historical-Jew...124583&sr=11-1

                            http://books.google.com/books?id=ex9...#PRA1-PA317,M1

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                            • #15
                              jloe, thanks for the references. I hope my point was clear. If one is going to estimate back from the population at a later date to the population at an earlier date, one must look at all descendants not just those who remained Jewish, given the pressure to convert. In my own case, there were close non-Jewish dna matches in Germany but not from any other European country.

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