Great analogy Ghokun! I think that at beginner and intermediate levels genetics plays a very minor role, instead, effort and dedication will determine your success. Even at elite levels perseverance keeps some athletes in classes they should not be in based solely on their genetics (slow metabolism, small frame, etc.) Don't use genetics as an excuse to give up.
I know some doctors who perform tests that can tell you what you're genetically predisposed to weigh. I'm not sure if it's possible for it to be accurate, but it does sound interesting. I haven't tried it yet because it's so expensive. I mean it's very pricey and student health insurance won't cover it.