5.5 Environmental Effects on Phenotype

Learning objectives

5.5A—Explain how the same genotype can result in multiple phenotypes under different environmental conditionsExplain how the same genotype can result in multiple phenotypes under different environmental conditions.• Environmental conditions influence gene expression and can lead to phenotypic plasticity (e.g., the ability of individual genotypes to produce different phenotypes).

Phenotypic plasticity is the ability of one genotype to produce different phenotypes under different environmental conditions. The DNA sequence remains the same, but the environment changes how the genotype is expressed.

Causal chain: environmental condition changes a cellular or organismal signal → expression of particular genes increases or decreases → protein abundance or activity changes → the observable phenotype changes.

For example, soil pH can influence flower color in plants with the same genotype, and seasonal conditions can influence fur color in arctic animals. In each case, environmental input changes the expressed trait rather than creating a new inherited allele.

To test an environmental effect, compare individuals with the same genotype under different values of one environmental variable while holding other conditions constant. A consistent phenotype difference supports an environmental contribution; comparing different genotypes would confound inherited and environmental effects.

A phenotype change does not by itself show that the genotype changed. Phenotype reflects genotype, environment, and their interaction.

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