Answer
1. Neither allele has complete dominance over the other.
2. The heterozygote has a phenotype that is intermediate between the phenotype of the homozygous dominant and that of the homozygote recessive.
Work Step by Step
A well-known case of incomplete dominance is encountered in the inheritance of hemoglobin, the oxygen carrying protein of the bood(RBCs). Normal hemoglobin is coded for by the HbA gene which is dominant. There are several other hemoglobin genes including the thalassemia gene and the gene for the sickling hemoglobin (HbS).
A person who has the hemoglobin genotype HbA/HbA produces normal hemoglobin(A). A person who has the genotype HbS/HbS makes only hemoglobinS, and is said to have the blood disorder called sickle cell anemia.
Some of the manifestations of this disease are fragile, short-lived RBCs, poor growth, chronic pain, swollen hands and feet, chronic fatigue, and frequent infections. The HbA gene and the HbS gene are alleles, but neither is completely dominant over the other. Therefore, a person with the genotype HbA/HbS does not have sicle cell disease, neither is he/she normal . Such a person is said to carry the sickling trait. Under conditions of oxygen stress such an one will display-- in a mild forms-- some of the signs and symptoms associated with sickle cell anemia. This is a classical case of incomplete dominance.
