Chapter 8, Problem 11RQ

The ABO blood groups in humans are expressed as the $I^A,I^B$ and $i$ alleles. The $I^A$allele encodes the A blood group antigen, $I^B$ encodes B, and $i$ encodes O. Both A and B are dominant to 0. If a heterozygous blood type A parent $\left(I^{A}i\right)$ and a heterozygous blood type B parent $\left(I^{B}i\right)$ mate, one quarter of their offspring are expected to have the AB blood type $I^A{I}^B$in which both arnigens are expressed equally. Therefore, ABO blood groups are an example of:

a. multiple alleles and incomplete dominance

b. codominance and incomplete dominance

c. incomplete dominance only

d. multiple alleles and codominance