Genealogy /
Jewish Roots of Poland [638]
It was a cultural thing, Nobles saw mixing with Jews as degradation
Bullsh*t. Lots of noble families intermarried with Jews (for example Radziwiłłowie, Potoccy, Lubomirscy, Lanckorońscy and Hutten-Czapscy) and Jews were often ennobled themselves.
I also disagree with Yehudi's conviction that a Jew would rather die than convert. According to the Polish law "Jeśliby Żyd który albo Żydówka do wiary chrześcijańskiej przystąpili, tedy każda osoba i potomstwo ich za szlachcica poczytywani być mają"
Meaning that every Jew who converts automatically became a noble and his family did too.
Here's an interesting article about the Jewish Neophytes (with nice drawing of their coats of arms if anyone's interested):
rp.pl/artykul/139640.html
But of course, that's only the nobles. They made up no more than 10% of the population so it's still not enough to significantly change the gene pool of the whole nation. Certainly not many peasants intermarried with Jews.