1. The problem asks about the dominance relationships in the ABO blood type system. 2. The ABO blood group system involves three alleles: A, B, and O. 3. Important genetic concepts: - Dominant allele: an allele that expresses its trait even if only one copy is present. - Codominance: both alleles express their traits equally when present together. - Incomplete dominance: the heterozygous phenotype is a blend of the two alleles. 4. In the ABO system: - A and B alleles are codominant, meaning both are expressed when present together (genotype AB). - O allele is recessive to both A and B, meaning it is only expressed when two O alleles are present. 5. Therefore, the correct statement is: - "A and B are codominant." 6. Explanation: - If a person inherits allele A from one parent and allele B from the other, both A and B antigens are expressed on red blood cells. - O does not produce antigens and is recessive. Final answer: 2. A and B are codominant.