In incomplete dominance, the dominant allele is unable to express completely over the recessive one. Hence it results into blending of the traits. For example, in Mirabilis jalapa when red flowers (dominant trait) are crossed with white flowers (recessive trait), the red colour of the flowers are unable to express completely, thereby resulting into formation of pink flowers (blended trait).

Whereas, in codominance, neither of the two alleles is recessive. Both the alleles are equally dominant and are able to express themselves independently. Hence, the resulting phenotype expressed is a combination of both the parental phenotypes. For example, codominance seen in blood group AB. The alleles I^A and I^B which are responsible for blood group A and B respectively, when present together express equally. And the resultant allelic combination becomes I^A and I^B, and the expressed phenotype is blood group AB.