Do a websearch for the Lemba. They are Blacks in southern Africa who have a cultural tradition resembling Judaism. Their legends say they are descended from traders who were away from home, when the news of the fall of their homeland reached them -- so they stayed where they were and married locals... Black Africans.
Genetic tests on their Y-chromosomes indicate that indeed, their Male ancestors were largely Semitic, not Sub-saharan African. Furthermore, the "priestly" tribe of Lemba has many Y-chromosomes of the "Cohen Modal Haplotype"... In short, they really are Jews!
Not me, though... I'm a goy. My Irish mtDNA is identical to Helena's (no mutations in 20,000 years) and my Scottish Y chromosome is 2 single-step mutations away from the Atlantic Modal haplotype (descended from the Stone-Age colonists of Western Europe.)
It was with the so-called "Jewish Gene" projects that the research "irregularities" were discovered. Check recent threads here on FR for lots of details.