What type of inheritance involves more than two alleles for a trait?

The correct answer is related to the concept of multiple alleles, which occurs when more than two alternate forms of a gene exist for a particular trait within a population. Instead of having just two alleles (one from each parent), traits governed by multiple alleles can exhibit a range of expressions because of these varying alleles.

An example can be seen in the ABO blood group system, where there are three different alleles: A, B, and O. Individuals can have various combinations of these alleles, which results in different blood types (A, B, AB, or O). The presence of multiple alleles increases the genetic diversity and potential variations of traits within a population.

In contrast, other concepts like co-dominance and incomplete dominance describe how alleles interact rather than the number of alleles present. Co-dominance occurs when both alleles in a heterozygote are fully expressed, while incomplete dominance results in a blended phenotype. Pleiotropy refers to a single gene affecting multiple traits, which is a different aspect of genetics altogether. Therefore, the term "multiple alleles" precisely describes the situation where more than two alleles influence a single trait.