Wikia

Transbreed Aliens are described as Aliens who take characteristics, major or minor, from their hosts. They are the opposite of Purebreed Aliens, who take nothing from their hosts and emerge as one Alien variant regardless of what their facehugger infected.

The term Transbreed and Purebreed was first used in Aliens versus Predator: Extinction, but is only a game mechanic. The Xenomorph species has no base form due to mutations and different hosts being used and it's unknown if they ever had one.