Which blood type would be completely recessive to the other types within the ABO blood group system?

In the ABO blood group system, blood type O is completely recessive to the other blood types. This means that for an individual to exhibit the O blood type, they must inherit the O allele from both parents (genotype OO). The O allele does not produce any specific antigens on the surface of red blood cells, which distinguishes it from blood types A and B, both of which have their own respective antigens (A antigen and B antigen).

Conversely, blood types A and B each can be present with the O allele in heterozygous forms (genotype AO for type A and genotype BO for type B), which express the A and B antigens respectively. Blood type AB (genotype AB) expresses both A and B antigens, as it has neither an allele linked to type O nor is it capable of being recessive since both codes for the presence of antigens.

Thus, type O stands out as the only blood type that does not exhibit dominance over other types, making it the completely recessive blood type when considering the ABO blood group system.