Card 10 / 16: The ABO blood groups in humans are expressed as the IA, IB, and i alleles. The IA allele encodes the A blood group antigen, IB encodes B, and i encodes O. Both A and B are dominant to O. If a heterozygous blood type A parent (IAi) and a heterozygous blood type B parent (IBi) mate, one quarter of their offspring will have AB blood type (IAIB) in which both antigens 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

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