Utah State Human Development Practice Test

Polygenic traits are those that are influenced by multiple genes, typically two or more. This characteristic is fundamental because such traits arise from the additive effects of various alleles contributing to the phenotype. For example, traits like height, skin color, and intelligence are determined by the combined influence of several genes, each contributing to the overall phenotype in a cumulative manner.

Focusing on the other choices, a single gene controls traits governed by Mendel's laws, leading to simpler inheritance patterns. The option stating "all genes in the genome" oversimplifies the genetic basis of polygenic traits. Finally, environmental factors do play a role in the expression of traits, but in the context of polygenic inheritance, the primary factor remains the action of multiple genes. This distinction helps clarify the nature of polygenic traits and their genetic complexity.