Today is National DNA Day. DNA testing has become increasingly popular for genealogy purposes, and the Jewish community is no exception to this trend. This is clear from this year's IAJGS conference on Jewish Genealogy , which is boasting in-depth DNA workshops and has more than 20 lectures related to DNA on its schedule. But DNA testing for genealogy purposes poses a special problem for Jews, often called the Ashkenazi Problem: Jews tend to marry Jews, and Jews who do not marry Jews tend to drop out of the Jewish community, and we have been doing that for so long in such a small population that we all tend to have a lot of DNA in common. The technical term for this is "endogamy," or in other words, inbreeding. As a result, one study found that the average Jewish DNA tester matched 54% of all testers with any Jewish heritage! Compare this with gentile testers, who matched less than 1% of all testers with gentile ancestry. But if you are Jewish and interested ...