The genetics course at my university was at the 200-level. Not upper-division.
There were advanced genetics courses, of course, taught upper-division, but they aren't necessary.
Personally, I found having the intro genetics class to be extremely helpful because the MCAT probably will have some genetics questions. I don't find these questions too difficult after having the genetics course, but I can't imagine trying to learn about test-crosses, mutations, dominant/recessive traits, etc on my own.