Well actually it's more like it's on my grandmother's side. My grandmother (my dad's mom) is the oldest relative alive that I know who stutters, although hers is now very mild. My grandfather did not stutter. So in my case, it's clearly passed down on the X chromosome / mitochondrial DNA from grandmother, which why it's so strongly expressed in my family. That's just my speculation. But also my grandmother had kids with another man (also a non-stutterer) before my grandfather and those kids did not stutter. So it seems it also depends on the genetic make up of the other partner, if the kids stutter. How the combination of the genes express themselves in the children.