Don't just look at your mom's dad, consider your mothers brothers as well.
Because it is a genetic thing that gets most of its phenotype from the X gene in the XY world, it makes sense to look at her brothers.
So your mom gave you an X and your pops gave you a Y. Your mom has XX. So, you don't know which X you got. Let's say the first X came from your grandma and the Second from your grandpa. So your grandpa has a full head of hair. Sweet. That accounts for the second X and your clear and free there. But that first X is still a mystery. Perhaps your grandmother carried the trait... Does your mom have brothers? Are any of them bald? If so, then it is likely she was a carrier of the balding X. So, maybe grandma had to balding X's or maybe she only had 1 balding x. In which case, if your mom's brothers are bald, there is at least a 25% chance that you will acquire grandma's balding gene.
Of course none of this is 100% proved yet. They believe there are multiple genes that cause baldness.
-genetics junky.
