Not just genetics, but also our gut microbiome. The studies linking depression and other thinking to our gut bacteria raise some profound moral implications.
I've had really interesting conversations with some of the gay people I know where I've urged them to at least start thinking about what would happen if science found a biological or genetic basis for homosexuality. If human sexuality can be altered with a probiotic, targeted antibiotic or gene therapy, the LGBT community should be prepared for the renewed attack on their way of life that would bring. Just because they intuitively consider it part of their identity doesn't mean that it is biologically so. Science isn't going to avoid investigating or finding these kinds of things, no matter how much opinion shifts towards acceptance of non-majority sexual preferences.
I can also envision a world in which increased understanding of the mechanics of our sexuality poses some interesting moral questions and scenarios. What if all sexual preferences are governed by these mechanics, not just gender? Even straight people have a wide variety of preferences when it comes to race, body type and other physical characteristics. Could surreptitiously trying to alter someone's preferences be considered rape in much the same way that using GHB to bypass consent currently is? Could we have a world where gene therapies to increase compatibility become part of marital counseling? Might 23andme.com become the world's best online dating site? Might people in cultures with arranged marriages start forming the arrangements pre-birth and then selecting embryos for IVF based on the compatibility of their offspring?
This field of study offers so many really interesting /r/WritingPrompts for near-future science fiction writers. So many of our institutions, customs and culture revolve around the propagation of the species that demystifying it could really turn society on its head in some interesting ways.