If identical twins are considerably more similar than fraternal twins (which is found for most traits), this implicates that genes play an important role in these traits.By comparing many hundreds of families with twins, researchers can then understand more about the roles of genetic effects, shared environment, and unique environment in shaping behavior.A soft butch, or stem (stud-fem), is a woman who exhibits some stereotypical butch and lesbian traits without fitting the masculine stereotype associated with butch lesbians.
"Fraternal" or dizygotic (DZ) twins share only about 50% of their genes, the same as any other sibling.
, but the heroine is much more likely to end up happy this way.
However, it creates a problem insofar as the heroine has to neither fight her common sense nor reform the hero for a Happy Ending.
Note that this isn't Always Female as Single Man Seeks Good Woman can certainly be in play. As this trope frequently deals with critical plot details, be warned: HERE THERE BE SPOILERS.
Some are unmarked, too, so don't say we didn't warn you.