I believe Aranea actually suggests that the Beforan trolls were created from the genetic mix of the Alternian trolls, rather than just being clones. Chiefly by suggesting she is Terezi's "ancestor" almost as much as she is Vriska's in their first conversation.

True, but then we’d have to start playing who was mixed with who. Which while it may be fun, can lead to some angry fans. So let’s not go there just yet.

~Mod T