<em>A. involves the expression of both alleles at a locus producing two different phenotypes.</em>
Explanation:
Codominance is the expression of both alleles, and is the result of a heterozygous expression. Let's say a white and red flower produce offspring, if the offspring come out with white with red spots, then it will be codominant. Both of the colors are present in the offspring, without mixing. Incomplete dominance is the mixing of the colors, so if the offspring came out as pink, it would be incomplete dominance.
