Which term describes inheritance where multiple genes contribute to a trait, producing a continuous range of phenotypes?

• A. Monogenic inheritance
• B. Epistasis
• C. Polygenic inheritance with additive effects
• D. Pleiotropy

Answer: (C)

Many traits show a smooth spectrum because many genes each contribute a small amount to the overall outcome. This pattern is described as polygenic inheritance with additive effects. Each gene adds a little to the trait, and when you combine all those small contributions across many genes, you get a continuous range of phenotypes rather than only distinct categories. Height is a classic example: dozens or more loci influence it, and the final height is the sum of many small genetic effects plus environmental influences.

In this view, the gene-by-gene contributions add up in a roughly additive way, so shifting one gene’s contribution slightly changes the phenotype, and the population ends up with a broad distribution.

Other terms don’t fit this pattern as cleanly. Monogenic inheritance involves a trait controlled by a single gene with discrete outcomes. Epistasis refers to interactions between genes where one gene’s effect depends on another’s, which can complicate the pattern and isn’t the standard explanation for a normally continuous range. Pleiotropy means one gene affects multiple traits, not how many genes influence a single trait or how that trait varies continuously.

So, polygenic inheritance with additive effects best explains a trait that shows a continuous range of phenotypes due to the combined influence of many genes.