Sometimes you can't tell! ... My husband, who seems like a pretty bright guy (he's a lawyer) drinks beer and likens himself to Homer Simpson; he always would say our younger one takes after his (ungifted) side of the family!
My wife was the same way (minus the beer and Homer). Since I'm the nerd in the family, she assumed our DD takes after me. Then we started reading about giftedness to understand what we had with DD, and suddenly my wife started noticing things about her brother and his boys that fit the profile.
Not that I was surprised... I remembered what she'd done early in our marriage when she took an interest in cooking that bordered on obsessive. It started out with Food Network nearly 24x7, cookbooks wherever she could find them, constant experimentation, and ended up with a full-time cooking school, where she stood far above the rest of her classmates. Classic gifted behavior.