User blog comment:Jed Revenant man/Female Space Marines, or, "Can of Worms, opening."/@comment-1536954-20110108020420

The emperor had 12 male sons. Its the 41st millennium, sexism has died just like much of humanity's knowledge of how to recreate technology. Males would obviously be viewed as the strongest, in fact its genetical.

There is a a large difference between the Space Marines and Sisters Of Battle. The Sisters are the ordo millitant of the Ordo Hereticus (Witch Hunters), so they are primarily intended for the cleansing of heretics and unsactioned psykers and etc. They are up in the same place as say the Deathwatch and Grey Knights.

The Space marines are superhuman warriors designed to fight against any threat that apposes the Imperium with lightning fast speed. They are up there with the imperial guard.

So... technically, battle sisters aren't the female counterparts of the Adeptus Astartes, but they are the closest thing to.