If two persons with 'AB' blood group marry and have a sufficiently large number of children, these children could be classified as A blood group : AB blood group : B blood group in 1 : 2 : 1 ratio. Modern technique of protein electrophoresis reveals the presence of both 'A' and 'B' type proteins in 'AB' blood group individuals. This is an example of:

In codominance, neither phenotype is completely dominant. Instead, the heterozygous individual expresses both phenotypes. A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. The A and B alleles are codominant with each other. When a person has both A and B, they have type AB blood. In codominance, it doesn't matter whether the alleles in the homologous chromosomes are dominant or recessive. If the homologous chromosome consists of two alleles that can produce proteins, then both will be produced and forms a different phenotype or characteristics to that of a homozygote.