I'm mixed....black and white. I'm a 3b/3c mix. Almost every one of my siblings is mixed with something....not all of them have curly hair. Lets see:

Mexican/white brothers --> all of them had adorable baby curls...but their hair went straight after a year or 2

moroccan(arab)/white brother --> he has a little wave when its longer

Navajo/black brother --> Aparently his curls are a little looser than mine, so probably a 3A or 3b

white/Poly??/Black sister --> somewhere between me and the native brother. so probably a solid 3b

Most of the mixies I know that are part black have some sort of curl. but theres more types of mixes than that. Most of the hair fall somewhere in between their parents.