Most of my DNA explorations have centered around my Dad’s Norwegian DNA because so many Norwegians have tested and the populations of those ancestors are only mildly endogamous; so it is easy to find new cousins and fun to work with those results.
My mother’s father was a German Jew. The number of DNA matches this gives me, my brother, and my two maternal aunts is astronomical. Frequently I will match someone from Eastern Europe for five or six large segments who cannot share an ancestor with us for the last 200-300 years and is even listed as a “distant cousin.” If they were Norwegian, that amount of shared DNA would make them my 2nd cousin.
This has been so frustrating that I just about stopped working on my Jewish DNA. A fellow Jewish researcher told me to ignore matches who did not have at least one 23cM shared segment!
Today there were dozens of news articles about the European Jewish founder effect suggesting that all Ashkenazim are descended from about 350 people who lived in about 1300 A.D. or so. This, combined with a fair amount of endogamy, would explain the large amount of shared DNA among European Jews.
These articles are all based on a study published online at Nature Communications (nature.com) by Shai Carmi with a group of people including his mentor, Itsik Pe’er, a cofounder of the Ashkenazi Genome Consortium (TAGC – notice those letters!). Professor Pe’er is an associate professor of computer science at Columbia and a consultant for 23andme.
TAGC has collected the full genomic sequence for 128 healthy ashkenazim from many cooperating sources to create a data resource for studying diseases specific to this group. However this collection has far more uses, including the study of the founding population of European Jews.
Here are some of the key findings and points of that published study:
- The founding population for Ashkenazim of a few hundred in about 1300 A.D. was about half middle eastern and half European.
- Europe was largely repopulated by people from the near east after the last glacial maximum.
- There are more disease causing mutations in Ashkenazi DNA than in European DNA, an effect of the small founding population followed by genetic isolation.
- This data resource, the 128 genomes, will allow better understanding of jewish mutations that are not harmful as well as the disease causing ones.
The article that best summarizes this study for us laymen is this one from the Times of Israel: http://www.timesofisrael.com/ashkenazi-jews-descend-from-350-people-study-finds/ Enjoy!