Final answer:
Incomplete dominance is when the phenotype of the heterozygote is a mix of the homozygous phenotypes, while codominance is when both alleles are equally expressed in the heterozygote, as seen in human blood types.
Step-by-step explanation:
When comparing incomplete dominance and codominance, we are looking at two different patterns of inheritance where neither allele is completely dominant over the other.
In incomplete dominance, the phenotype exhibited by the heterozygote is intermediate between the phenotypes of the homozygotes. For instance, when a red-flowered plant is crossed with a white-flowered plant, the offspring might have pink flowers, which is an intermediate, or blended, phenotype between the two parents.
On the other hand, codominance refers to a situation where both alleles for a gene are expressed equally in the heterozygote. A classic example of codominance is the human ABO blood group system. Individuals with the AB blood type have both A and B antigens on the surface of their red blood cells because both alleles (IA and IB) are expressed simultaneously.
In summary, both incomplete dominance and codominance involve situations where traditional dominant/recessive inheritance does not apply, but they differ in the heterozygous phenotype.