How does codominance differ from incomplete dominance?

The distinction between codominance and incomplete dominance lies primarily in how alleles interact in the phenotype of the organism. In codominance, both alleles contribute equally and visibly to the organism's appearance, leading to a phenotype where both traits are expressed simultaneously. This is exemplified in cases like the ABO blood group, where individuals with AB blood type display characteristics of both A and B antigens on the surface of their red blood cells.

The correct answer highlights this key characteristic of codominance, emphasizing that both alleles are fully expressed in the phenotype, allowing for clear expression of both traits without blending. This stands in contrast to incomplete dominance, where neither allele is fully dominant over the other, resulting in a blended phenotype that does not represent either allele distinctly.

In this context, the other options provide useful information about how codominance and incomplete dominance function but do not directly capture the essential difference that the correct answer outlines. For instance, while it is true that both conditions involve traits influenced by two alleles, the fundamental impact of codominance is its ability to jointly express traits without blending. The specificity of codominance applies in broader contexts than just ABO blood types; it can also refer to other genetic traits where both alleles are