I'm father to an ambidextrous, red-headed girl, and a left-handed son (who can usually pass for "normal"). I also have a left-handed grandson so it's apparent that I've passed along my 'sinister' genes.
As far as I know, I’m the only left-hander in the family. Neither parent nor grandparents were left-handed, so I don’t know what happened. I’m just glad I was born in a more modern time, or I wouldn’t have survived.