Genetics is a trip, isn't it?
And I agree with what BC said about how genes might mix together to come up with the pheonotype of your hair texture. For instance, I don't know anyone in my family who has the hair texture that I do. In the family there is either straight or wavy hair or just straight up afro, kinky hair. However, my hair is like somewhere in the middle of the extremes but closer to the kinkier side.
Basically, with genetics you can't be sure of what you're going to get. That's why you shouldn't be too alarmed when two black parents with white ancestors from way back create a child that may come up with hazel or green eyes. The probability of that happening might be low but there is still a chance.
That's why I cannot understand why a black person will say that they want to marry a white person so that their kids can have straight, wavy, or mildly curly hair. Those kids' hair might still come out afro-textured.
Regarding growth, retention for looser textures is generally easier. But with tighter curled hair, you just need more patience and you REALLY have to love your hair!
-Ebony