Codominance, as it relates to genetics, refers to a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual. That is, instead of one trait being dominant over the other, both traits appear, such as in a plant or animal that has more than one pigment color.
Codominance. In people, one codominant trait that you can't really observe by looking at a person, but many people know about themselves, is blood type. People with the AB blood type have one A allele and one B allele. Because both alleles are expressed at the same time, their blood type is AB.
Precision Genomics Section