Ahh well if you look at what is said in the game, everyone already has cetra genes, because the whole human race was decended from a section of cetra society that settled down and stopped listening to the planet.

So going on my theory of Cloud being a neo-cetra, he's kind-of a throwback - a human who has learnt how to listen to the planet again, at least moreso than most humans that exist, and thereby can access more of the planet's power (magic, in other words) than the average human.


It probably also helps that he's been practically soaked in mako a few times in his recent life though.