Thus a person whose genetic type is either AA or AO will have blood
type A, those with genetic
type BB or BO will have blood
type B, and only those with genetic
type OO will have blood type O. This means that a child with type O blood could have parents with type A, type B, or type O blood (but not with type AB). Conversely, if two parents both have type O blood, all their children will have type O blood.
Another medically important blood type is described in the Rh system.