What are the four major blood types found in humans?

ABABO

O−o+a−a+b−b+ab−ab+

They are O, A, B and AB which are phenotype and AA/AO, BB/BO, AB, OO which are genotype

O, A, B, and AB. Each can be Rh positive or negative.

A, B, AB, and O. If you want to go more specific with the Rh factor, which is positives and negatives, there is: A+, A-, B+, B-, AB+, AB-, O+, O- with AB+ being the universal recipiant: this means...