Red blood cells carry antigens on their surfaces coded for by alleles of the gene designated by the letter I. IA is dominant to i and produces antigen A on the surface of red blood cells. The IB allele is also dominant to the i allele and produces antigen B on the surface of red blood cells. The i allele does not produce surface antigens. The Human Blood Types are shown.

What types of inheritance are represented by the genetics of human blood types? Select all of the answers that apply.
A. IA and IB show incomplete dominance because both alleles are partially expressed in blood type A and B.
B. The human blood types are an example of polygenic traits with four possible phenotypes: A, B, AB, O.
C. IA and IB show codominance because both alleles are equally expressed in blood type AB.
D. The human blood type gene is an example of a gene with multiple alleles, IA, IB, i.