What characterizes traits controlled by multiple alleles?

Traits controlled by multiple alleles are characterized by the presence of three or more different alleles for a particular gene within a population. This concept means that while an individual organism can only inherit two alleles (one from each parent) for any given gene, the total genetic variation available for that trait in the population is much greater due to the presence of multiple alleles.

For example, the ABO blood group system in humans illustrates this principle. There are three alleles: A, B, and O. The combination of these alleles can result in four different blood types: A, B, AB, and O. The existence of multiple alleles allows for a broader range of phenotypes to be expressed, enhancing genetic diversity within a population.

The other options do not accurately describe the nature of traits regulated by multiple alleles, as they either limit the number of alleles or misrepresent genetic concepts entirely.