So this is the blood type alley. Now as we mentioned earlier, the Abo blood group locus is located on the chromosome number nine. And each allele is passed down from each one of the two parents. Now as it turns out, the blood type is a codominant train, a codominant trait. And what that basically means is if one parent gives an antigen A gene while the other parent gives an antigen B gene, they will both be expressed on that red blood cells membrane. And what that means is if this is A and this is B, when they combine they will form the AB blood type group.