In Humans:
* ABO blood group: The ABO blood group system is a classic example of codominance. There are three alleles for the blood group: A, B, and O.
* A and B are codominant: Individuals with genotype AA or AO have blood type A, and individuals with genotype BB or BO have blood type B. Individuals with genotype AB have both A and B antigens on their red blood cells, resulting in blood type AB.
* O is recessive: Individuals with genotype OO have blood type O.
* Sickle Cell Anemia: The gene for hemoglobin has two alleles: the normal allele (HbA) and the sickle cell allele (HbS).
* HbA and HbS are codominant: Individuals with genotype HbA HbA have normal hemoglobin. Individuals with genotype HbS HbS have sickle cell anemia. Individuals with genotype HbA HbS have both normal and sickle-shaped red blood cells. This condition is called sickle cell trait.
* Tay-Sachs disease: This genetic disorder is caused by a mutation in the HEXA gene, which is responsible for producing an enzyme that breaks down a fatty substance called GM2 ganglioside.
* Both alleles are expressed: Individuals with one normal copy of the gene and one copy of the mutated gene will have a reduced amount of the functional enzyme and may have a milder form of the disease.
* Coat color in Roan Cattle: Roan cattle have a mixture of red and white hairs.
* Both alleles are expressed: This occurs because the red hair allele (R) and the white hair allele (W) are codominant. The heterozygous genotype (RW) results in both red and white hairs.
In Plants:
* Flower color in Snapdragons: Snapdragons can have red flowers, white flowers, or pink flowers.
* Red and white are codominant: The red allele (C^R) and the white allele (C^W) are codominant. The heterozygous genotype (C^R C^W) produces pink flowers.
* Fruit color in strawberries: Strawberries can have red, white, or yellow fruits.
* Red and yellow are codominant: The red allele (R) and the yellow allele (Y) are codominant. The heterozygous genotype (RY) produces orange fruits.
In Animals:
* Coat color in Shorthorn cattle: Shorthorn cattle can have red, white, or roan coats.
* Red and white are codominant: The red allele (R) and the white allele (W) are codominant. The heterozygous genotype (RW) produces a roan coat, with a mixture of red and white hairs.
These are just a few examples of codominance in living organisms. This pattern of inheritance is important because it allows for greater diversity and complexity in the traits of organisms.
