Genetics Extensions of Mendelian Inheritance Practice Test 2025 - Free Practice Questions and Study Guide on Mendelian Inheritance Extensions

The mode of inheritance that is commonly associated with ABO blood types is codominance. In the ABO blood group system, there are three alleles: A, B, and O. Both A and B alleles are dominant over the O allele, but when an individual inherits both A and B alleles, they express both traits equally, resulting in type AB blood.

This occurs because neither allele masks the expression of the other; instead, both are present and contribute to the phenotype. This phenomenon of both alleles being fully expressed is a hallmark of codominance, distinguishing it from other forms of inheritance such as complete dominance, where one allele completely masks the presence of another, or simple recessiveness, where the recessive allele does not manifest in the phenotype when a dominant allele is present. Coclassical inheritance is not a recognized term in genetics, further reinforcing that codominance is the correct concept for explaining the inheritance of ABO blood types.