The answer is incomplete dominance.
In incomplete dominance, heterozygous phenotype is
intermediate between two homozygous phenotypes. In this case, the symbols for
alleles are capital letters. For example, allele A is responsible for red color
of a flower, allele B is responsible for white color of the flower. Red flower
plants have AA genotype, and white flower plants have BB genotype. By crossing
plants with red flowers and white flowers, due to incomplete variance, the
offspring will be heterozygous plants (AB) with neither red nor white flowers,
but pink flowers. Pink flowers have intermediate color between red and white
flowers.
It should be distinguished from codominance in which both alleles are expressed in heterozygous conditions. In incomplete dominance, alleles are blended in heterozygous conditions.
