AP Biology 5.5: Environmental Effects on Phenotype

Phenotypic plasticity

Phenotypic plasticity is the ability of one genotype to produce different phenotypes in response to different environmental conditions. The changes may involve morphology, physiology, behavior, or developmental timing and may be temporary or long-lasting.

How phenotypic plasticity differs from genetic differences between individuals

Plasticity allows the same genotype to respond differently in different environments, whereas inherited genetic differences can cause different genotypes to produce different phenotypes under the same environment. Phenotype generally reflects both genetic information and environmental influence.

Polyphenism

Polyphenism is a form of phenotypic plasticity in which environmental differences induce distinct, discrete phenotypes rather than a continuous range of variation.

Reaction norm

A reaction norm describes the range of phenotypes that a single genotype can produce across different environmental conditions. It illustrates how environmental variation can affect phenotype without changing genotype.

How environmental factors influence phenotype

Environmental factors such as temperature, nutrition, light, and chemicals can alter gene expression, protein activity, development, or physiology. These changes can modify the phenotype even when the organism's genotype remains unchanged.

Acclimation and phenotypic plasticity

Acclimation is a reversible physiological or morphological adjustment to environmental conditions during an individual's lifetime. It is one form of phenotypic plasticity and does not require a change in genotype.

Temperature-dependent sex determination

In some reptiles and other animals, the temperature experienced during embryonic development influences whether an individual develops as male or female. Thus, environmental temperature can affect a major phenotype despite the organism's genetic information.

Phenylketonuria as an example of environmental effects on phenotype

Phenylketonuria results from mutations that impair phenylalanine metabolism. A diet low in phenylalanine can prevent or greatly reduce the associated neurological effects, demonstrating that nutrition can modify the phenotype produced by a genotype.

How light can affect phenotype in plants

Light can influence plant gene expression, growth direction, leaf development, and the timing of flowering. These environmentally induced responses are examples of phenotypic plasticity.

Why a phenotype is not always determined by a single gene

Phenotype generally results from interactions among multiple genes and environmental conditions. Environmental factors can alter gene expression or protein activity, while genes can function together in developmental or biochemical pathways.