This one should be a slam dunk. Unlike race, where the genetics and biology are, shall we say, fraught, I highly doubt anyone here will deny that genetics/biology plays at least some role in determining one's gender. Likewise, is there anyone here who would deny that gender--what it means to be a man vs a woman--is influenced at least in part by the culture in which one is raised? Methinks gender roles are simply too variable--across both culture and time--to argue otherwise.
So while we could argue forever regarding the relative contributions of nature vs nurture in determining gender, I don't think anyone could reasonably argue that both don't play at least some role in its determination. (That said, reasonableness is at times in short supply, so...)