In genetics, what best describes traits that are controlled by multiple alleles across multiple loci?

The best description of traits that are controlled by multiple alleles across multiple loci is continuous variation. Traits exhibiting continuous variation are typically influenced by the additive effects of several genes, known as polygenic inheritance. This results in a range of phenotypes rather than discrete categories. For example, human height is a classic example where multiple genes determine the overall height, leading to a continuous spectrum of heights rather than just a few set points.

In contrast, multiple alleles refer specifically to a situation where more than two alleles exist for a given gene. While multiple alleles can contribute to variation, they do not necessarily imply that the trait is influenced by multiple genetic loci. Environmental variation involves changes in phenotype due to environmental factors rather than genetic ones. Autosomal traits refer to traits determined by genes located on autosomes, not limited to a method of inheritance. Hence, the concept of continuous variation most accurately captures the essence of traits controlled by multiple alleles across multiple loci.