**Core Concept**
The ABO blood group system is a classic example of a polygenic trait, where the expression of the ABO gene is influenced by multiple genetic and environmental factors. The codominant inheritance pattern of ABO blood groups is determined by the interaction of two alleles, A and B, at the ABO gene locus on chromosome 9.

**Why the Correct Answer is Right**
The ABO gene encodes for the ABO blood group antigens, which are glycoproteins present on the surface of red blood cells. The A allele codes for the A antigen, while the B allele codes for the B antigen. The O allele is a recessive allele that codes for no antigen. When an individual inherits the A or B allele, they will express the corresponding antigen on their red blood cells. However, when an individual inherits the O allele, they will not express any antigen, resulting in type O blood. The interaction between these alleles determines the individual's ABO blood group.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided. Please disregard.

**Option B:** This option is not provided. Please disregard.

**Option C:** This option is not provided. Please disregard.

**Clinical Pearl / High-Yield Fact**
The ABO blood group system is a crucial consideration in transfusion medicine, as incompatible blood types can lead to hemolytic reactions. It is essential to determine the ABO blood group of the donor and recipient before transfusion to ensure compatibility.

**Correct Answer: D. Codominant inheritance**