I don't have any known (alive or dead) Jewish ascendants, but I think the reason why I have Sephardic blood is because Sephardics typically mixed in with the rest of the population in Iberia (which is where most of my DNA comes from)
Most likely none. I come from a family of poor serfs and peasants so it's impossible for me to have blood of rich merchants and bankers.
Maybe back in the medieval era there were some jews in my family, but class differences would probably not allow it.