That's what I was thinking! Genes don't evolve in a vacuum, they evolve together. So if you disrupt half the chromosome with some negroids watermelon digestion enzyme, your kids gonna have all kinds of issues by default. (aside from the obvious that niggers are dumb and aggressive and your kid would inherit this)
From what I gather, hybrid vigor only works when farmers have "inbred" individuals, only selected for their traits, not general fitness or genetic distance. So I really don't understand the genetic *benefit* for 6th cousins over brother and sister. I can't count the number of homestead videos and wildlife docs I've seen where this happens and I have never seen them lament a cronenbergian aberration that spawned from it.
Maybe someone crunched the numbers somewhere but I've never seen it.