What best defines dominance effects in genetics?

Dominance effects in genetics refer specifically to the interactions between alleles at a single locus. This concept explains how different alleles can influence the phenotype of an organism when present together. For example, if one allele is dominant over another, it will determine the trait that is expressed in the phenotype, regardless of whether the second allele is present.

This approach to understanding dominance focuses on how one allele can mask the expression of another at the same genetic locus, resulting in a specific observable trait. Because of this interaction, understanding dominance effects is critical in genetics, as it helps clarify how traits are inherited and expressed in offspring.

The other choices touch on different genetic interactions. Interactions between genes across different loci, and the total genetic architecture affecting behavior, involve more complex relationships that go beyond the concept of dominance, often including epistasis and polygenic traits. The choice related to only recessive alleles does not encompass the broader definition of dominance effects, as dominant alleles can also significantly influence expression when present. This makes the selection of the interactions between alleles at one locus the most accurate definition of dominance effects in genetics.