Everything I can add is strictly theory on my part; no scientific evidence. From my 17 years (not long at all compared to some) of messing with Show Calves, I have come to believe their dispositions are much like humans. I feel like their environment has much more to do with how they act and react than does their genetics. If you have seen the movie, The Horse Whisperer, that's what I mean. We are around the calves constantly from birth; always moving slowly, and quiently, with no sudden moves, and absolutely no correction by force or anger. Our cows, calves, and bulls are all tame as Lap Dogs. My next statement conflicts with the last because it has much to do with Genetics, but not the Bull. I can not remember one single time that a calf has not had virtually the same temperament as it's Dam. The cows are calm, therefore the calves react in the same way. Baby see, baby do.
All in all, my feeling is two fold concerning cattle dispositions. Calves from calm Dams will have good dispositions, and if they are gently broke, pampered, and cared for, they will remain good tempered. In the wrong hands, any of them can go bad. My advice is never buy a calf without seeing the Dam. If she has her head in the air, and eyes glazed, don't buy her calf.