Which characteristic is true for traits governed by multiple alleles?

The correct choice highlights that traits governed by multiple alleles involve the presence of more than two alleles for a specific gene. This means that within a population, there are various forms of the gene, which can lead to a variety of phenotypic expressions when combined in different ways. A prime example is the ABO blood group system in humans, which has three alleles: A, B, and O. Each individual carries two alleles, but because there are three possible alleles in the population, the resulting blood types demonstrate the characteristic of multiple alleles effectively.

In contrast, options that suggest only two alleles exist or that only codominance can occur are not applicable as they don’t encompass the complete nature of multiple alleles. While codominance can occur in systems with multiple alleles, not all traits governed by multiple alleles display this pattern, as some may exhibit complete dominance or incomplete dominance. The mention of "none of the above" does not provide an adequate description, as option B accurately captures the essence of multiple alleles. Thus, the presence of more than two alleles is central to understanding how genetically diverse traits can be expressed and inherited within a species.