What best defines a polygenic trait?

• A. A trait influenced by many genes, typically showing continuous variation.
• B. A trait controlled by a single gene with complete dominance.
• C. A trait determined entirely by environmental factors with no genetic influence.
• D. A trait expressed only in males.

Answer: (A)

Polygenic traits come from the combined action of many genes, each contributing a small amount to the overall phenotype. This additive effect creates a wide, continuous range of trait values rather than distinct categories. Height is a classic example, as it varies gradually across a population and is also influenced by the environment. In contrast, traits controlled by a single gene with complete dominance produce discrete outcomes (like purple vs white flowers) rather than a smooth spectrum. If a trait were determined entirely by the environment with no genetic input, there would be no genetic basis for variation. And traits expressed only in males are typically sex-limited or sex-linked, not polygenic in the classic sense.