In which type of inheritance does the combined effect of two or more genes influence a single trait?

The combined effect of two or more genes influencing a single trait is best described by polygenic inheritance. In this type of inheritance, multiple genes contribute to the phenotype, resulting in a continuum of traits rather than distinct categories. For example, human skin color, height, and eye color are influenced by several genes, each adding a small amount to the overall trait.

In contrast, incomplete dominance and codominance involve interactions between alleles of a single gene rather than multiple genes. In incomplete dominance, the phenotype is a blend of the two alleles, while codominance occurs when both alleles are expressed equally in the phenotype. Pleiotropy, on the other hand, refers to a single gene affecting multiple traits, which is the opposite of polygenic inheritance. Thus, polygenic inheritance accurately captures the scenario of multiple genes working together to determine a single trait.