Back when Lebanon was in the news a lot because of the civil war, one Christian family which was often mentioned was the Franjieh family. Their name means they claim descent from the “Franks”—the general term for Western Europeans. In other words, they are descended from the Crusaders.
I'm descended from the same couple on both sides of my family (three times -- that I know of) and despite the passage of a mere 400 years, there's no DNA trace of that relationship. The loss of half of the available possible DNA is actually what makes sexual reproduction more viable than, say, parthenogenesis, in complex multicellular organisms. :^)