Many Americans don't know their blood type, but that knowledge can actually tip you off about your risk for certain medical ...

The ABO system also has a distinction as Rh-positive which decides A+, B+, O+ and AB+ blood type and Rh-negative, which leads ...

However, this system presented a number of problems ... For example, a man who has type AB blood could not father a child with type O blood, because he would pass on either the A or the B allele ...