Final answer:
Incomplete dominance occurs when the heterozygote exhibits a phenotype intermediate between the two homozygotes, while codominance occurs when both alleles are expressed equally. For example, in a cross between a red and a white flower, the heterozygous offspring may have pink flowers (incomplete dominance). In humans, individuals with blood type AB have both the A and B phenotypes equally (codominance).
Step-by-step explanation:
Incomplete dominance describes situations in which the heterozygote exhibits a phenotype that is intermediate between the homozygous phenotypes. For example, if a red flower (homozygous) and a white flower (homozygous) are crossed, the heterozygous offspring may have pink flowers. This is because neither the red allele nor the white allele is completely dominant over the other.
Codominance, on the other hand, occurs when both alleles for the same characteristic are simultaneously expressed in the heterozygote. For instance, in humans, the A and B alleles for blood type are codominant, resulting in individuals with blood type AB expressing both the A and B phenotypes equally.