In the ABO blood group system, which genotype corresponds to a person with type O blood?

In the ABO blood group system, a person with type O blood has the genotype OO. This is because the A and B alleles are codominant and will express the phenotypes of type A or type B blood when present. Type O blood, which lacks both A and B antigens on the surface of red blood cells, occurs when an individual inherits two O alleles, one from each parent. Thus, the presence of two O alleles is required to express the type O phenotype, making OO the only genotype that corresponds exclusively to type O blood.

In contrast, the genotypes AA and AB would result in the phenotypes of type A and type AB blood, respectively, while the BB genotype corresponds to type B blood. Therefore, OO is the correct and only genotype for individuals with type O blood in the ABO blood group system.