Dear Rabbi Simon,
How do Jewish people brought up in a traditionally religious Jewish family generally score on DNA tests such as from “My Heritage”?
Thank you for your enquiry.
I do not know the answer to your question, as I am not aware of any research that has been done in this area. It is not unusual for people who suspect or seek to verify Jewish ancestry (including Jewish halakhic status) to make use of DNA testing as a means of exploring their roots. However, such evidence, while potentially interesting and helpful in some ways, is rarely compelling, much less definitive, in terms of halakhic status. The reason for this is that Jewish status in determined by the maternal side specifically. This means that a woman (or a man) with one Jewish grandparent may be Jewish, while a man with three Jewish grandparents may not be. Also, the phenomenon of conversion introduces (heretofore) non-Jewish DNA into the genetic record. So Jewish status is not a matter only of race and/or ethnicity.
Finally, the contemporary phenomenon of assisted conception and surrogate motherhood further complicates the question of halakhic status vis a vis the genetic record.
I hope these general observations, while not answering your question directly, are still of interest.
Rabbi Rashi Simon