Bra size (girls and guys) :D

Ok so I live in where the caucasian race in the majority and the african americans are the minority. Now, I am Irish, Scottish, White (not sure), Native American, Bermudian (Father), French, and African. White people tend to have a smaller chest size (naturally lol) and blacks are larger. I'm a size D and 14 whereas my sister is a size B and is 17! I'm just wondering about certain things that's all...