Marissa! Hi!!!!
I'd recommend selling it if you're not going to be taking more genetics courses, if you're saving your notes, and/or if most of the information is google-able. It also depends how useful you found the textbook. Personally, I don't find textbooks THAT useful, I'm not doing any more genetics, and I should be able to google anything I need to know or I can look it up in my biochem textbook, so I'll be selling it.
ps---we finished our course just in time! Dr Dej had her baby (a girl) yesterday morning