Quantitative traits and continuous variation When a character displays continuous variation with an approximately normal distribution in a population, which statement best explains the genetic basis?

Introduction / Context:Traits such as height, yield, or skin color often vary continuously and approximate a bell-shaped curve. These quantitative traits reflect polygenic inheritance and environmental influences.

Given Data / Assumptions:

• Distribution is continuous and near-normal.
• No single discrete classes dominate the phenotype.
• Environmental effects may contribute but do not fully explain the pattern.

Concept / Approach:Polygenic traits result from many loci, each with small additive effects. According to the central limit tendency, the sum of many small, independent genetic contributions plus environmental noise yields a normal-like distribution, consistent with observed quantitative traits.

Step-by-Step Solution:

Verification / Alternative check:Biometric analyses (heritability, QTL mapping) consistently reveal multiple loci with small effects underlying quantitative traits.

Why Other Options Are Wrong:

• “Not controlled genetically”: contradicts QTL evidence.
• “Climate only”: environment contributes but cannot alone produce consistent heritable distribution.
• Single-gene complete dominance: would yield discrete classes, not smooth normal curves.

Common Pitfalls:Attributing all variation to environment; overlooking additive genetic variance.

Final Answer:It is governed by many genes with small cumulative effects (polygenic)