There’s something fishy about the way that storytellers generally construct gender and sexual identities within the realms of sci-fi and fantasy. For fantasy, more oftentimes than not, gendered constructions are old-school, even, dare I say, medieval. For sci-fi, this is where you find society streamlining into a more androgynous “look,” as everything is sleeker, shinier, more utilitarian/egalitarian — or, on the post-apocalyptic side, grittier and more unrelenting in the face of forces that don’t care what pronoun you use, so long as you can survive in the Battle Royale-esque free-for-all landscape.
But this makes mapping out notions of romance within these genres very interesting. For instance, take a look at “Lord of the Rings” and its main forms of romance. They’re all heterosexual, generally traditional (the character Eowyn is an anomaly, but with reservations — she is still vying for male affection, in the end), and focused on the idea of romance as an everlasting bond: you get married to the person you love and end up with them forever!!! There are plenty of other stories that fit that traditional medieval fantasy mold, even if they aren’t set in a vaguely medieval universe. Hell, even mainstream fantasy narratives that exist in modern or almost-modern times don’t play around that much with that dynamic, but the precedent is almost always followed to a T in anything with knights and kingdoms and that ilk (with one dramatic mainstream exception — more on that later).
Then with sci-fi, or perhaps more fittingly, future-oriented shows with a scope beyond just humanity, somehow these differences in gender/sex dissolve into much more fluid forms. Women in shows like “Star Trek” have equally important professional roles (though those uniforms, while kicky, are definitely segregating). Beyond that, sci-fi often introduces humanoid beings that don’t always reproduce, and thus have secondary sex characteristics, as humans do — and thus do not have sexual relationships as humans do. Though sex and romance do not always have to be linked, the fundamental differences in the former do have an impact on the expression of the latter.
Of course, these are all broadstroke observations, and the line between sci-fi and fantasy isn’t clear at all, especially if you’re trying to define what is alien versus fantastically supernatural. But when you look at a media property, be it a short story or a TV show, you can generally “tell” what genre the story is nested in, and thus the genre conventions that might be at play. The Marvel film universe, though certainly grounded in a sense of fantasy, is much more of a sci-fi franchise; thus, it expresses itself as more of a future tech-oriented, gender/sex egalitarian universe. Meanwhile, something like “Twilight,” though rooted in the real world, is observably a fantasy narrative (albeit a… shaky one).
But where things get really interesting, in so many ways, is when a narrative takes genre conventions and subverts them. A really great example: George R.R. Martin’s “A song of Ice and Fire” epic (“Game of Thrones” the show… while its own good thing, not so much). The romantic relationships in AsoIaF are epically subversive, and Martin takes on gender/sex constructions with a pleasantly surprising amount of nuance. Sure, the sexual dynamics are still quite skewed, but the characters’ knowledge of and interaction with those dynamics are some of the most interesting relationships in the story. And, as the success of the series and its TV spinoff show, these subversions, if done within the context of a solid narrative, can be just as gripping as the archetypes embedded in genre conventions.