What is the genetic condition in which the heterozygous individual has different phenotype from the homozygous individual?

This condition is called lack of dominance and it can occur in two ways: incomplete dominance or codominance.

In incomplete dominance the heterozygous presents an intermediate phenotype among the two types of homozygous, as in sickle cell anemia in which the heterozygous produces some sick red blood cells and some normal red blood cells. Codominance occurs, for instance, in the genetic determination of the MN blood group system, in which the heterozygous has a phenotype totally dissimilar from the homozygous, not being an intermediate form.

Image Diversity: incomplete dominance codominance