The ABO blood type is a trait that demonstrates which type of inheritance?

• A. Incomplete dominance
• B. Polygenic inheritance
• C. Complete dominance
• D. Codominance

Answer: (D)

Verified step by step guidance

1. Understand the concept of codominance: Codominance is a form of inheritance where both alleles in a gene pair are fully expressed, resulting in offspring with a phenotype that is neither dominant nor recessive. In the case of ABO blood types, both A and B alleles are expressed equally in individuals with AB blood type.
2. Review the ABO blood group system: The ABO blood group system is determined by the presence or absence of antigens on the surface of red blood cells. The A and B antigens are encoded by different alleles of the same gene, and the O allele does not produce any antigen.
3. Identify the alleles involved: The ABO blood type is controlled by three alleles: I^A, I^B, and i. The I^A allele codes for the A antigen, the I^B allele codes for the B antigen, and the i allele results in no antigen (O type).
4. Examine the expression of alleles: In individuals with AB blood type, both I^A and I^B alleles are present and expressed equally, demonstrating codominance. This means that neither allele is dominant over the other, and both contribute to the phenotype.
5. Compare with other inheritance patterns: Unlike complete dominance, where one allele masks the expression of another, or incomplete dominance, where the phenotype is a blend of both alleles, codominance allows both alleles to be fully and equally expressed in the phenotype.