I just watched YJ and wondered if Vandal Savage was Genghis Khan does that mean that millions related to Genghis Khan have a higher change of having the metahuman gene?
Also is superboy metahuman if he gets his powers from the kryptonian DNA?
Superboy is not Metahuman. Young Justice follows the original, Invasion! era definition of "meta-gene", which is basically the same thing as the mutant gene from Marvel. Vandal is basically En Sabah Nur in this interpretation.