If you can fit it in your schedule, drop and retake it some other time. I was in your situation, and my GPA went from like almost 3.9 to 3.75, because of one damn class (yeah, it also diverted attention from other classes too, allowing their grades to suffer).
Obviously, don't say the prof was screwy. For a class like genetics, you can just say that you realized doing good in genetics was important since genetics is so fundamental to medicine and bio (yada yada.. something like that). So, you were doing somewhat poorly in the class, and you wanted to make sure you had a good background with such fundamental stuff. And, that's not all big talk either, genetics IS important for almost anything in bio.
Your other choice might be to file pass/ no pass.
seriously, when you have a very high GPA (i.e. >3.85) you are opening yourself for a lot of opportunities at top tier schools. (please do not try to attack this w/ comments on how GPA isn't all medschools are looking for... there is basis f or this, and you want to know, PM me). So, it's worth preservng.
your prof was probably crappy in some ways, but realize, the fact that you're doing bad is probably making you think more negative of him than he really is.
sonya