autosomal codominant inheritance

Last reviewed 01/2018

Autosomal codominant inheritance is defined by the ability to detect either or both of two alleles in an individual. The two fragments can also be followed through the family pedigree. Hence, the pedigree pattern of human codominant traits resembles that of autosomal dominant inheritance except that both alleles can be distinguished.

Some examples of human codominant traits include:

  • blood groups: ABO, Duffy, Kell, Kidd, MNS, Rhesus
  • red cell enzymes: acid phosphatase, adenylate kinase
  • serum proteins: haptoglobulins
  • cell surface antigen: human leucocyte antigen (HLA)

Autosomal codomominant inheritance can be demonstrated if consider ABO blood groups:

  • if two persons with AB blood type have children, the children can be type A, type B, or type AB
  • the possible phenotypes are
    • A, AB and B
    • there is a 1A:2AB:1B phenotype ratio - this compares with a 3:1 phenotype ratio found when one allele is dominant and the other is recessive