If both parents are Rh-positive but carry one Rh-negative allele, there's a 25% chance they could have an Rh-negative child. Your blood type—A, B, AB, or O—is determined by the ABO system and ...

and AB positive or AB negative. O positive blood is the most common blood type in the United States; approximately thirty-eight percent of the United States population has this type. Individuals ...