What is the genetic condition in which the heterozygous individual has different phenotype from the homozygous individual?
This situation is called lack of dominance and it can happen in two ways: incomplete codominance or dominance.
In the incomplete dominance the heterozygous presents an intermediate phenotype between the two kinds 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 example, in the genetic determination of the MN blood group system, in which the heterozygous has a phenotype totally different from the homozygous, not being an intermediate form.