Unfortunately, I can't ask them, as my mother has passed away, and my father will not talk about it. The fact that my Dad wasn't interested in genetic testing

Unfortunately, I can't ask them, as my mother has passed away, and my father will not talk about it. The fact that my Dad wasn't interested in genetic testing was my first hint, as that is very unlike him. But it makes sense in the larger pattern- I am the youngest of the family by 15(!) years, and all of my siblings were adopted. It seems pretty clear in retrospect that my parents likely had to use a sperm bank. I've had my suspicions for a while, so this wasn't the complete shock it could have been. Still threw me for a loop at first, though.