Seems like it's really tricky to determine what is and is not genetic, or primarily genetic. If you work with your own line for example, and they are ALL outstanding markers, can you be sure that it's actually the dog, or maybe something you do or don't do with your pups, or in training, or components of both maybe.
I think speed of maturity (or maturity level by age) is genetic and can influence how you think a dog marks or does other things before you get into "training" something in or out of them. Wouldn't that complicate evaluating some of the other things from a genetic or environment standpoint?
Someone above also brought up a good point in that the pup's position in the litter and the puppy experience before you get them has a huge influence as well.
I'd think sitting with crossed front legs is something genetic too, except that all of my dogs do that and they're not related, heck one's a little yappy dog, so maybe it's just comfortable?
It's an interesting question for sure.
There was a post awhile back about the genetics of marking, and some discussion about marking itself not being genetic, but that many of the traits that go into marking (from great to poor) are most certainly genetic - eyesight for example.