Which example illustrates codominance?

Which example illustrates codominance?

• A. Pink flowers result from mixing red and white to form pink (incomplete dominance).
• B. AB blood type shows both A and B alleles expressed.
• C. A trait masked by a dominant allele (complete dominance).
• D. A trait only expressed when homozygous recessive.

Answer: (B)

Codominance is when both alleles in a heterozygous individual are expressed fully in the phenotype. The ABO blood group system is a classic example: having one A allele and one B allele leads to red blood cells that show both A and B antigens on their surface, producing AB blood type. This demonstrates that neither allele masks the other; each contributes its trait. In contrast, an intermediate phenotype like pink flowers results from incomplete dominance, where the heterozygote blends the traits rather than expressing both. So the AB blood type best illustrates codominance because both alleles are expressed simultaneously.

Codominance is when both alleles in a heterozygous individual are expressed fully in the phenotype. The ABO blood group system is a classic example: having one A allele and one B allele leads to red blood cells that show both A and B antigens on their surface, producing AB blood type. This demonstrates that neither allele masks the other; each contributes its trait. In contrast, an intermediate phenotype like pink flowers results from incomplete dominance, where the heterozygote blends the traits rather than expressing both. So the AB blood type best illustrates codominance because both alleles are expressed simultaneously.