What does it mean to be genetically Jewish?

Oscar Schwartz in The Guardian:

This genetic explanation of my Ashkenazi Jewish ancestry came as no surprise. According to family lore, my forebears lived in small towns and villages in eastern Europe for at least a few hundred years, where they kept their traditions and married within the community, up until the Holocaust, when they were either murdered or dispersed.

But still, there was something disconcerting about our Jewishness being “confirmed” by a biological test. After all, the reason my grandparents had to leave the towns and villages of their ancestors was because of ethno-nationalism emboldened by a racialized conception of Jewishness as something that exists “in the blood”.

The raw memory of this racism made any suggestion of Jewish ethnicity slightly taboo in my family. If I ever mentioned that someone “looked Jewish” my grandmother would respond, “Oh really? And what exactly does a Jew look like?” Yet evidently, this wariness of ethnic categorization didn’t stop my parents from sending swab samples from the inside of their cheeks off to a direct-to-consumer genetic testing company. The idea of having an ancient identity “confirmed” by modern science was too alluring.

More here.