Question

What do you mean by codominance? Explain it with example of blood groups in human beings.

Answer 1

• Codominance is a heterozygous condition in which both alleles at a gene locus are fully expressed in the phenotype. Alleles which show an independent effect are called as Codominant alleles. In codominance, neither phenotype is completely dominant.
• The best example of codominance is ABO blood group. ABO blood grouping is controlled by gene I which has three alleles A, B, and O and show codominance. An O allele 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 does not 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.