Gendercide in SF
Gendercide is the deliberate destruction of all the members of one sex/gender of a species.
It has been portrayed in SF a number of times; also, many post-gendercidal societies have been shown; see men-only worlds and women-only worlds. Sex wars might be intended to effect gendercide.
Gendercide should be distinguished from (a) real-life situations in which one sex or another is disproportionately favored (i.e., sex-selective infanticide or abortion); the intent must be to eliminate a gender; and (b) accidental plagues that happen to be sex-selective.