Genderswap

The problem is exactly the one you have stated: many people would not be comfortable with a sudden genderswap in the Doctor, when the possibility has not even been hinted at in the past.

Source: wiktionary

But I liked the fact that they *were* friends and not lovers, as *the* most obvious thing to do with a genderswap of either Kirk or Spock is promptly pair them off together.

Source: wiktionary

More sober challenges to the representation of gender in mainstream media (and of course, Supernatural specifically) occur in genderswap stories where the sudden change of anatomy is one that throws the character's world into chaos.

Source: wiktionary

I am a completely unartistic person who has found myself in charge of a fanfic shared world project to genderswap Marvel mutants. Thus, Xavier and Magneto are women and always were; Storm and Rogue are men and always were; you get the idea.

Source: wiktionary