I don't believe the mothers dad stuff...at least in every case. My grandfather died with a thick full head of hair, and both of my brothers are thinning starting in their mid twenties
my brother that is 4 years younger is bald on top and is only 33 (took after fathers father). I have a full head of hair like our mothers father.
just luck of the draw I guess. Though, like my brother, if I get to that point sometime in the future, I'm just shaving it off.
I'll just compensate by growing the beard out and braid it like the crazy Viking fella's hahaha.