Which term describes the combined effect of multiple genes on a single trait?

The term that describes the combined effect of multiple genes on a single trait is polygenic inheritance. In polygenic inheritance, several different genes contribute to the phenotype of a single trait, resulting in a continuous variation of phenotypes rather than discrete categories. This is observed in traits such as height, skin color, and weight in humans, where multiple genes interact and influence the outcome.

In polygenic traits, each gene may have a subtle effect, and together they can produce a wide range of phenotypic expressions. This model of inheritance contrasts with traits that are determined by a single gene, which typically exhibit clear, distinct phenotypes.

The other options represent different genetic concepts. Epistasis refers to the interaction between different genes where the effect of one gene is dependent on the presence of one or more 'modifier genes,’ rather than multiple genes contributing to a single trait. Genetic drift is a mechanism of evolution that involves random changes in allele frequencies in a population, unrelated to the impact of multiple genes on a specific trait. Chromosomal aberration refers to structural changes in chromosomes, such as deletions, duplications, or translocations, and does not specifically describe the interaction of multiple genes affecting a single trait.