Possible Duplicate:
How do Muggle-borns end up with magical ability?
Was it ever clarified how magic is passed on hereditarially so that both children of two wizards or half bloods can both be fully magical?
Possible Duplicate:
How do Muggle-borns end up with magical ability?
Was it ever clarified how magic is passed on hereditarially so that both children of two wizards or half bloods can both be fully magical?