We could artificially create human "breeds" with pedigrees, and a lot of this goes on with inbreeding and nobility. If we really wanted to play the game of "purebreds" versus "mongrels" in the human sphere, we could. But for the most part, we don't want to.
When it comes to typifying humans by genetic makeup, there're so many ways to slice and dice. Why aren't dwarves a race, or albinos? We say "genetic anomaly" or whatever, but any genetic characteristic might be lumped into a breed or "race" by convention, should we wish it.
We could easily have "races of human" based on blood type only. This would satisfy no one of course, because the whole point of racism is to have distinguishable outward characteristics that allow one to be classified. Like if you speak Italian as a first language, you're obviously of the Italian race and so on. :-D
