Okay, this may have just popped in my head because it's interesting and possibly real or I have had way too much elvin grass in my pipe but, is being born with the talent of magic but not just pairing with one of the third race being but also a recessive gene in human?

It would explain why some are born from family lines with no magic users in it. It would also explain why families with long and full magic users have the occasional child with no magic. As well as why the odds are more than just 50/50 for children of one magic user and one non magic user. What do you think?