First, I don't think there is a genetic thing with anger and abuse. That is something that is learned. Example: My grandfather physically and verbally abused my dad growing up. My dad never laid a hand on my sister or me like that -- but he kind of went the other direction and withholds a lot of emotions and has a problem opening up.
And yes, like Laura K. I was going to say that mental illnesses can be passed on in families, but even then with the right meds and therapy the person can learn/be taught the right way to act.
A lot of the anger is just from him being this particular age and not being able to verbalize. A lot of it is him trying to exert control over things, because as we all know toddlers are pretty much directed by parents, teachers, etc. They want to be soooo independent but they also crave rules and boundaries. Without them they feel lost and out of control.
What I have started doing with my 4yo DD is talking to her before we go on an outing and specifically stating how she must behave, and what will happen if she doesn't. Like, "Remember, in the restaurant we all have to sit in our chairs and use inside voices. If we get in there and you won't stay in your chair or get loud, we're going to go have a little talk in the bathroom. Understand?" That way she knows exactly how to act and exactly what will happen if she doesn't mind.
At home, I usually put her into this corner where nothing else is there but her. Lately, though, she has been really bucking going into that corner. Soooo, I have been taking priviledges away. So if she throws a fit or doesn't mind me, fine. No playing outside/drawing at your art table/TV - whatever is the biggest thing right then. After doing that a few times she knows I'm not playing around.
Most of all, just love him! I know sometimes I get busy and that's when DD shows out a little more. But if I remember to sit down and read or play w/her, even for 30 min., it's really interesting how things run smoothly!