Genetics have nothing to do with muscle size.
Any healthy human can build big muscles with exercise, food and drugs, or a decently thick ass w/o drugs.
Show me a juiced up chick who works out her ass with squats and whatever else, who doesn't have a thick juicy ass.
I fucked a pretty-jacked fbb with a flat/tiny/muscleless ass once... she told me she didn't squat because she injured herself. I wasn't surprised.
Btw, I didn't give her a cent and it actually costed her (hi Halo

)