I’ve been reluctant to address this issue for two reasons. First, aspects of it lie beyond my qualifications. Second, I will have to cover a considerable amount of discussion when in the end I think the whole question is irrelevant to the modern period.
The aspects that are beyond my expertise are the various discussions of the genetics of people who self-identify as Jews. I do have in-house expertise on the matters–as most of you know, my wife is a bona fide expert on genetics, so I can turn to her for questions I might have about the various published studies. So let’s dabble a bit in that area and see what we can discover.
One aspect of the discussion is fairly obvious to me given that I am a carrier of the Tay-Sachs disease. Tay-Sachs is a terrible affliction, 100% fatal before the age of 4, but requires transmission by two carriers. In other words, I couldn’t father a Tay-Sachs child unless I married another carrier, in which case the odds would be 1 in 4.
References: Ostrer H, Skorecki K. The population genetics of the Jewish people. Hum Genet. 2013 Feb;132(2):119-27. doi: 10.1007/s00439-012-1235-6. Epub 2012 Oct 10. PMID: 23052947; PMCID: PMC3543766.