College Board-Aligned Original Notes

AP Biology Unit 5 Topic 4: Environmental effects on phenotype

Phenotype results from genotype interacting with environmental conditions, so the same genotype can produce different outcomes.

Unit 5: Heredity. College Board exam weighting listed for this unit: 8%-11% of exam score.

What to Know

Environmental factors such as temperature, nutrition, light, stress, and chemicals can affect trait expression.
Some environmental effects change gene expression without changing the DNA sequence itself.
Complex traits often reflect combined genetic and environmental influences.
Always connect this topic back to the larger unit: Heredity.

Detailed Notes

Environmental effects on phenotype belongs to Unit 5: Heredity. Phenotype results from genotype interacting with environmental conditions, so the same genotype can produce different outcomes. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Environmental factors such as temperature, nutrition, light, stress, and chemicals can affect trait expression. Some environmental effects change gene expression without changing the DNA sequence itself. Complex traits often reflect combined genetic and environmental influences.

Model to use: Use a reaction norm graph to show how different genotypes respond across an environmental gradient. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: If a prompt compares genetically similar organisms in different conditions, explain how environment changes expression of inherited potential. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Phenotypic plasticity

The ability of one genotype to produce different phenotypes in different environments.

Norm of reaction

The range of phenotypes a genotype can produce across environmental conditions.

Epigenetic mark

A chemical modification that affects gene activity without changing DNA sequence.

Temperature-sensitive phenotype

A trait expression pattern that changes with temperature.

Multifactorial trait

A trait shaped by multiple genes and environmental factors.

Quick Practice

How would you explain Environmental effects on phenotype in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.