I took the April MCAT this year and if I'm not mistaken the Orgo is about 40% of the BS portion of the MCAT.
When it comes to genetics, yes it shows up frequently on the MCAT, but not always dealing with molecular genetics or mendelian genetics, etc...
In other words, genetics was a theme in the passage, but it tested you on concepts other than strictly genetics, such as physiology, etc...
Just know the fundamental concepts of molecular genetics and mendelian genetics, etc... don't worry about weird exceptions. Remember, it's a reasoning test, not a regurgitate test. So if you know you're concepts, rules, formulas (where applicable), you should be prepared.
Hope this helps