Co-dominance is a form of dominance wherein the alleles of a gene pair in a heterozygous condition are fully expressed. This results in offspring with a phenotype that is neither dominant nor recessive. A typical example showing co-dominance is the ABO blood group system. For instance, a person having A allele and B allele will have a blood type AB because both the A and B alleles are codominant with each other. Here neither of the two A or B allele is completely recessive or completely dominant.