Co-dominance Gene Interaction - When both alleles of a pair are fully expressed in a heterozygote, they are called co dominant alleles. Such alleles exhibit a unique pattern of expression with heterozygotes being phenotypically distinguishable from both of the homozygotes and expressing both alleles equally.

In general, two products are the same with respect to function but different in exact amino acid sequence. A phenotypic ratio of 1: 2 : has thus replaced the 3: 1 ratio because the alleles are both expressed in heterozygote, that is, the alleles are co dominant.