I cannot recall any thread discussing how particular talents (ie viels, certain elements, etc) are passed. There have been long ones about how the Magical gift itself is passed, mostly focusing on the whole random vs matrilineally, etc. We know that there is /something/ specific about a person that affects whcih types of magic they can use; Luccio is the perfect test case for that, but now that you mention it Ive never seen the why/how of that part discussed. Per WOJ magic talent is in most ways just like any other natural born talent; it still takes training, a no-talent person can still train decent skill, and a prodigy can still suck without practice, etc. So my guess would be that it is an odd and inexplicable mix of Nature vs Nurture, just like talent at sports or music.
Still, Id be interesting in seeing that discussion
