incomplete dominance

In genetics, incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes. This means that neither allele completely masks the other, resulting in a blended appearance. For example, crossing red and white four-o'clock plants produces pink offspring. If these pink plants are crossed, the next generation will show a ratio of red, pink, and white flowers. This indicates that the genetic information for red and white was not lost but rather expressed in a blended form in the heterozygote.1

This is distinct from codominance, where both alleles are expressed equally and simultaneously. An example of codominance is the human MN blood group system, where individuals with both M and N alleles display both antigens on their red blood cells.2