Okay, it's maybe not so much a genre as it is one movie. I can't think of another horror film who's storyline involves it's main character transforming from one sex into another.
Sure, there are a few cross-dressing movie villains out there, and the odd fellow who slaughters women so he can dress up in their skins (gross). But full on sexual transmutation?
I don't think so. (There WAS a cheese-filled comedy in '95 called Dr. Jekyll and Ms. Hyde, but I'm talkin' HORROR here. Nuff said.)
Or... is it? If your memory/Google skills are better than mine and you can come up with another film or two that might fit into Gender Bender Horror, drop a line and I'll happily update my opinion AND (bonus) this post.
Anyway. Dr. Jekyll and Sister Hyde was done in 1971 by the Amazing, Fantastic, Retro-flick-alicious HAMMER FILMS. When I first saw the title I assumed it was an exploitation flick, but Hammer generally plays their horror pretty straight, so I was intrigued. And they did play it totally straight.
Which is what makes the film so fun. They play it just like Robert Louis Stevenson wrote it: Jekyll is earnest, Hyde is monstrous, and their downfall is tragic. Not a cheese-filled scene anywhere.
With maybe the exception of Hyde, upon finding herself a woman, fondling her own breasts for a minute or two. But what man among us wouldn't do the same, if placed in a similar situation? (If you DENY, you also LIE.)
The story is... well, we know the story 'cause it's - THE story: Dr. Jekyll and Mr. Hyde. We've seen it done a million times - with varying levels of faithfulness to Stevenson's novella. Let's see, according to the infallable Wikipedia, we've had:
Dr. Jekyll and Mr. Hyde (1910, 1912, 1920, 1920 again, 1920 a third time, 1931, 1941, 1973, 1981, 1985, 1989, 2002, 2008)
The Testament of Dr. Cordelier (1959)
The Two Faces of Dr. Jekyll (1960)
The Strange Case of Dr. Jekyll and Mr. Hyde (1968)
I, Monster (1971)
Dr. Jekyll y el Hombre Lobo (1972)
Dr. Heckyl and Mr. Hype (1980)
Edge Of Sanity (1989)
Jekyll & Hyde (1990, 1997)
Mary Reilly (1996)
Jekyll + Hyde (2006)
And that's just the more or less straight-on horror films.
Anyway. It's a good watch and an interesting take on the story. Competently produced, well acted and (a bit surprisingly) focused on the horror of the tale rather than on female nudity. You should see it.
THREE BENT BRAINS