Which type of genetic effect involves the sum of individual alleles equating to their combined effect?

The correct choice reflects the concept of additive effects in genetics, which are significant in understanding how traits are inherited. In additive effects, the overall phenotype of an organism results from the cumulative influence of individual alleles at different loci. Each allele contributes a portion to the trait, meaning that the total effect on the phenotype can be directly calculated by summing the contributions of each allele.

This type of genetic effect is particularly important in quantitative traits, where multiple genes influence the outcome. Since each allele contributes independently to the phenotype, the additive model facilitates predictions about how traits will segregate in offspring, which is foundational in fields such as breeding and population genetics.

The other concepts, such as non-additive effects, epistatic effects, and dominance effects, differ fundamentally in how genetic contributions interact. Non-additive effects involve interactions that do not simply sum to create the phenotype, while dominance effects describe cases where one allele masks the effect of another. Epistatic effects refer to interactions between different genes that can alter the expected phenotypic outcomes based on individual gene contributions. In contrast, additive effects provide a straightforward approach to understanding genetic contributions to traits, making this the correct answer.