Final answer:
Codominance is the inheritance pattern where both alleles are fully expressed in the heterozygous state, without blending, as seen in the MN blood group system in humans.
Step-by-step explanation:
The pattern of inheritance where both alleles are expressed in a heterozygous individual without blending is known as codominance. Unlike incomplete dominance, where a heterozygous genotype expresses a phenotype that is intermediate between the two homozygous phenotypes, codominance results in both alleles being expressed fully and simultaneously. A classic example of codominance is found in the MN blood group system in humans. Individuals who are heterozygous for the M and N alleles (LMLN) express both the M and N antigens on the surface of their red blood cells. Another well-known example of codominance is the ABO blood group system, where alleles for A and B blood types are both expressed in individuals with AB blood type.