The ABO blood type demonstrates which of the following inheritance patterns?

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

Answer: (A)

Verified step by step guidance

1. Understand the concept of codominance: In codominance, both alleles in a gene pair are fully expressed in a heterozygote, resulting in offspring with a phenotype that is neither dominant nor recessive.
2. Review the ABO blood group system: The ABO blood type is determined by the presence or absence of antigens (A and B) on the surface of red blood cells. The alleles involved are I^A, I^B, and i.
3. Identify the alleles: I^A and I^B are codominant alleles, meaning that if an individual inherits both, they will express both A and B antigens, resulting in an AB blood type.
4. Differentiate from other inheritance patterns: In complete dominance, one allele completely masks the other, while in incomplete dominance, the phenotype is a blend of both alleles. Polygenic inheritance involves multiple genes affecting a trait.
5. Conclude that the ABO blood type demonstrates codominance, as both A and B antigens are expressed equally when both alleles are present.