Mild stutter since I was 12, but where from? [advice] needed.

Mild stutter since I was 12, but where from? [advice] needed. Just wondering if anyone could help me out really, so my stutter is rather mild and I do not stutter all that bad to which I am very grateful but at the same time I am still really angry with .. life itself I guess you could say for posing such a disability upon me. But my question regards to the following: In my family, no-one that I know of stutters, my mum doesn't, my dad doesn't, my sister and 2 brothers don't, my grandma doesn't, my grandfather doesn't (he said that he did at a younger age, but this is yet to be verified). Essentially what I'm trying to say is, pretty much no-one in my family stutters to my knowledge and my stutter isn't that bad, of course I have my off days, but heh, who doesn't right? So why do I stutter at-all? Surely it cannot be genetic if my father and mother do not stutter? How far back do genes/genetics even go? Any advice on this matter would be greatly appreciated as I am rather dumbfounded surrounding this topic.