I’ve heard that in Askenazi populations there are several genetic dieases of the nervous systems that are only genrally found within that population (I think Tay-Sachs diease was one of them) or occur at a particularly high level compared to ther populations.
As for tribal descent, evidently it was seen fit to establish heritage through the mother, as that was seen as the most positive proof of ancestry in this case.
"…the specific genetic marker that “ONLY” the Kohaym have, not the rest of or the Jewish people in general – I spent lots of time tracking down the geneticists who did the research…"
This is not to dispute the studies done on Jewish Genes, although, no mention if any non-Jewish ME men were tested for the “Kohen Gene”. The only sites I found tended to minimise the significance of the above, or try to deny it indirectly:
Progress. The reason you are Jewish if your mother is Jewish is much more basic – it is stated “because you KNOW who your mother is” whereas there can be doubt as to who the father is – but to have a portion in eratz Israel in this world and the world to come and to determine where you will livein messianic times you must have tribal descent. And that comes only from a Jewish father. To see how serious this is taken read about Ezra and Heizakira and the banishment of the “half-Jews.” The doubt is a theoretical doubt, though, as it is assumed no Jewish woman would ever have relations with a non-Jew, as Commanded.