Sources of phenotypic variation Which statement best captures the origin of variation observed among individuals in a population?
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AVariation is caused by genes only
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BVariation is caused by the environment only
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CVariation can be caused by both genes and the environment
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DNone of the above
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EVariation is caused by random sampling error only
Answer
Correct Answer: Variation can be caused by both genes and the environment
Explanation
Introduction / Context:Phenotypic traits arise from the interplay of genotype and environment. Quantitative genetics partitions trait variance into genetic and environmental components, with possible interaction between them.
Given Data / Assumptions:
- Traits can be monogenic or polygenic.
- Environmental factors (nutrition, temperature, exposure) influence expression.
- Gene–environment interaction can further modulate outcomes.
Concept / Approach:Phenotypic variance (Vp) is often modeled as Vp = Vg + Ve + Vgxe + error, where Vg is genetic variance, Ve environmental variance, and Vgxe their interaction. Both sources contribute to observed differences.
Step-by-Step Solution:
Recognize that purely genetic explanations ignore environmental modulation (e.g., height depends on nutrition).Recognize that purely environmental explanations ignore heritable differences (e.g., eye color).Select the combined statement acknowledging both genes and environment.Verification / Alternative check:Twin and adoption studies demonstrate contributions from both heredity and environment to many traits.
Why Other Options Are Wrong:
- Genes only: fails for highly plastic traits.
- Environment only: fails for strongly heritable traits.
- Random sampling only: sampling affects estimates, not true causation of variation.
Common Pitfalls:Over-attributing complex traits to a single cause; ignoring interaction terms and developmental timing.
Final Answer:Variation can be caused by both genes and the environment