AP Psychology — Interactions of Heredity and Environment

Your genetic makeup — the set of genes you inherit.

Observable traits or behaviors — how genes are expressed under environmental influence.

The proportion of variation in a population’s trait that can be attributed to genetic differences.

Study of how genes and environment jointly shape behavior using twin and adoption studies.

MZ vs DZ comparisons estimate genetic contribution; adoption studies separate environment from heredity.

Study of how external factors switch genes on/off without altering DNA sequence (e.g., methylation).

Genes set upper/lower limits; environment determines where within that range a trait manifests.

Genes provide instructions, but environment and experience affect expression and outcome.

Heritability applies to population variation, not individuals—high heritability ≠ unchangeable trait.

Definition: rGE stands for gene–environment correlation—how an individual’s genetic makeup influences the environments they experience.

Different from G×E: rGE means genes shape exposure to environments, while G×E means the effects of genes depend on the environment.

Three types of rGE:

• Passive: Parents provide both genes and matching environments.
  Example: Musical parents pass on musical ability and fill the home with instruments.
• Evocative: A person’s traits evoke reactions from others.
  Example: A sociable child elicits more attention and praise.
• Active: People seek out settings that fit their tendencies.
  Example: A risk-taking teen joins extreme-sports peers.

Key idea: rGE creates feedback loops—genes influence behavior, which shapes environments that further reinforce those genetic effects.

Across many twin/adoption studies, Big Five traits commonly show moderate heritability (~40–60%). The remainder reflects environment, especially nonshared (unique) experiences. A simple way to remember:

Trait	Genetic (heritability)	Environment
Openness	~45–60%	~40–55% (mostly nonshared)
Conscientiousness	~40–50%	~50–60% (mostly nonshared)
Extraversion	~45–55%	~45–55% (mostly nonshared)
Agreeableness	~40–50%	~50–60% (mostly nonshared)
Neuroticism	~40–50%	~50–60% (mostly nonshared)

Teacher note: Ranges vary by sample, age, and methods; use these as ballpark figures to anchor discussion. High heritability does not mean “unchangeable.”

Typical genetic influence: ~45–60%. Environment: ~40–55%, largely nonshared.

• Hereditary/biological contributors (examples): Temperamental curiosity; neural networks supporting cognitive exploration and novelty processing.
• Environmental contributors: Enrichment/exposure (books, travel, arts/STEM clubs), teaching styles encouraging inquiry, diverse peer groups, cultural norms about creativity.
• rGE examples: Curious students may seek enrichment (active rGE); curious parents may provide stimulating homes (passive rGE).
• G×E idea: Enriched classrooms may amplify openness in students already inclined toward exploration.

Typical genetic influence: ~40–50%. Environment: ~50–60%, largely nonshared.

• Hereditary/biological contributors: Temperamental effortful control, self-regulation capacities, reward sensitivity for long-term goals.
• Environmental contributors: Family routines, study-skill coaching, academic expectations, sports/work responsibilities, feedback systems, sleep and health habits.
• rGE: Conscientious teens may choose structured activities that further train organization (active rGE).
• G×E: Skills programs (planners, checklists) may yield bigger gains for students with certain self-regulation propensities.

Typical genetic influence: ~45–55%. Environment: ~45–55%, largely nonshared.

• Hereditary/biological contributors: Baseline sociability/approach tendencies; sensitivity to social reward and positive affect.
• Environmental contributors: Peer networks, opportunities for leadership/performance, classroom climate for participation, family modeling of sociability, cultural norms.
• rGE: Sociable students evoke invitations/attention (evocative rGE) and join social clubs (active rGE).
• G×E: Supportive, low-threat contexts can enhance social engagement in those already dispositionally outgoing.

Typical genetic influence: ~40–50%. Environment: ~50–60%, largely nonshared.

• Hereditary/biological contributors: Temperamental warmth/empathy, threat reactivity and prosocial motivation systems.
• Environmental contributors: Parenting style (warmth/induction), conflict-resolution teaching, cooperative classrooms/teams, cultural expectations around politeness/helping.
• rGE: Warm, prosocial kids receive more positive peer responses (evocative rGE), reinforcing agreeableness.
• G×E: SEL programs may especially benefit youth with latent prosocial tendencies.

Typical genetic influence: ~40–50%. Environment: ~50–60%, largely nonshared.

• Hereditary/biological contributors: Temperamental negative affectivity, stress reactivity/sensitivity.
• Environmental contributors: Chronic stress, family conflict, peer victimization, sleep deprivation, coping skills training, therapy/CBT exposure, exercise.
• rGE: Highly reactive individuals may encounter (or perceive) more stressors, shaping environments that maintain anxiety/rumination.
• G×E: Stress-reducing interventions can have outsized effects for those with higher biological sensitivity to stress.

Teacher prompt: Ask: “Which of your guesses matched these patterns? Where did your life experiences push you away from your genetic ‘starting point’?”

• Law 1: All human behavioral traits are heritable (to some degree).
• Law 2: The effect of being raised in the same family is smaller than the effect of genes.
• Law 3: A substantial portion of the variation in complex human behavioral traits is not accounted for by genes or families (nonshared environment).

High heritability means within this population, given these environments, genes explain more of the variation—not that the trait can’t change.

Genes define a potential range; environment determines where outcomes fall within that range.

Task: Identify genetic factors, environmental differences, and how they interact; propose a simple study.

Task: Map diathesis–stress: genetic predisposition × home stress.

Task: Is this rGE (musical family) or G×E (lessons amplify disposition)? Likely both.

Task: Describe how methylation patterns may alter gene expression and potentially influence descendants.

Expected idea: The proportion of variation in a trait within a population attributable to genetic differences.

Scoring tip: Include “variation” + “genetic differences” for full credit.

Expected idea: Genotype = genetic makeup; Phenotype = expressed traits resulting from interaction with environment.

Misconception alert: Don’t say phenotype is “just genes.” Emphasize environmental influence.

Expected idea: Genes set upper and lower limits; environment determines the actual outcome within that range.

Extension: Provide an example (e.g. nutrition and height).

Expected idea: Environmental factor (e.g. stress, diet, toxin) that changes DNA methylation or histone state, altering gene expression.

Tip: Name both the environmental factor and its molecular mechanism or effect.