Question

The ABO blood groups in humans are controlled by 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, the ABO blood groups are an example of _______.

a) Codominance
b) Incomplete dominance
c) Polygenic inheritance
d) Pleiotropy

Answer 1

The ABO blood groups are determined by the alleles IA, IB, and i, with IA and IB being codominant. This codominance allows both A and B antigens to be expressed equally in AB blood types.

Step-by-step explanation:

The human ABO blood groups are determined by three alleles: IA, IB, and i. The A and B alleles (IA and IB) are dominant over the O allele (i) and express the A and B antigens on the surface of red blood cells, respectively. When both IA and IB alleles are present, as in blood type AB individuals, both antigens are expressed equally. This is because the IA and IB alleles are codominant to each other, and this codominance allows the distinct expression of both A and B antigens without blending. Therefore, if a heterozygous blood type A parent (IAi) and a heterozygous blood type B parent (IBi) mate, there is a one-quarter chance that an offspring will inherit the AB blood type (IAIB). This codominance, along with the presence of multiple alleles within the population, provides a wide range of possible genotypes and phenotypes in the ABO blood group system.