Buzzwords to anchor in your cortex: genotype vs. phenotype, reaction range, heritability, gene–environment correlation (rGE), epigenetics, shared/non-shared environment, plasticity.
Nature ≠ Destiny.
Your genotype is the full set of genetic code you inherit; your phenotype is the outward expression of those genes after the environment has had its say. Genes provide possibilities, environments decide probabilities.Reaction Range.
Think of genes as setting upper- and lower-bound “performance bands” (e.g., IQ 100-140). The environment (nutrition, schooling, stress) determines where within that band you land.Heritability (h²).
Statistic (0–1) telling us population-level variance attributable to genes in a specific environment.
Caveat emptor: High heritability does not mean an individual trait is “caused” by genes alone.
Gene–Environment Correlations (Scarr, 1993).
Type DNA’s Play Environment’s Counter-move Passive rGE Parents supply both genes and setting (musical parents give musical genes and a piano). Evocative rGE Child’s genetic tendencies elicit responses (smiley baby gets more social stimulation). Active rGE Child “niche-picks” environments that fit genotype (introvert chooses library over pep rally). Epigenetics — the switchboard.
Chemical tags (e.g., DNA methylation) can turn genes on/off in response to life events (diet, trauma). These tags can sometimes travel across generations (transgenerational epigenetic inheritance).Twin & Adoption Designs.
MZ twins > DZ twins similarity = genetic influence.
Adoptees more like biological than adoptive parents = genetic pull; the reverse implies environmental sway.
Shared vs. Non-Shared Environment.
Shared = factors that siblings experience together (same household SES).
Non-shared = unique experiences (different friend groups). Non-shared factors often explain why twins are not clone-level identical in personality.
Quick-Hit Cheat Sheet: Interaction of Heredity × Environment
(Swipe these bullets into your mental Notion board and move on.)
| 🔑 Concept | 1-Line Takeaway | “So What?” for AP MC/FRQ |
|---|---|---|
| Genotype vs. Phenotype | DNA is the blueprint; lived experience is the finished building. | Test writers love asking which one the environment tweaks (spoiler: phenotype). |
| Reaction Range | Genes set the high-low limits; environment decides where you land. | IQ, height, athleticism examples show up all the time. |
| Heritability (h²) | % of group variance tied to genes in that specific setting. | High h² ≠ “can’t change.” Expect a trick question here. |
| Shared vs. Non-Shared Environment | Same household ≠ same experiences. Non-shared usually beats shared for personality. | Use this to explain twin divergences. |
| Gene–Environment Correlation (rGE) | Genes guide which environments you get, elicit, or choose. | Know the trilogy—passive, evocative, active—and a quick example for each. |
| Epigenetics | Life events add chemical Post-its that silence or activate genes. | Buzzwords: DNA methylation, histone acetylation. Show off in FRQs. |
| Plasticity / Critical Periods | Neural wiring stays modifiable—especially early on. | Use this to argue why interventions still matter even with strong genetic pull. |
| Twin & Adoption Studies | The OG A/B testing for nature vs. nurture. | MZ twins > DZ twins similarities → genetics; adoptees like bio parents → genetics. |
| Canalization | Some traits (e.g., babbling) stay on track unless environment is extreme. | Low variance traits are often canalized—easy distractor eliminator. |
| Differential Susceptibility | “Orchid vs. dandelion” kids: some genotypes are extra reactive (good or bad). | If you see DRD4 allele + parenting style, think differential susceptibility. |
Practice Multiple-Choice Questions
(Format mirrors College Board style. Choose the best answer.)
Which concept best explains why genetically identical plants grow to different heights when placed in nutrient-rich versus nutrient-poor soil?
A. Heritability
B. Reaction range
C. Passive rGE
D. Kin selectionAdopted children’s IQ scores correlate more strongly with their biological parents than with their adoptive parents after age 16. This finding primarily supports the influence of:
A. Shared environment
B. Non-shared environment
C. Genetic factors
D. Prenatal teratogensA child genetically disposed to high activity levels tends to receive more negative feedback from teachers, which further shapes the child’s behavior. This illustrates:
A. Active rGE
B. Evocative rGE
C. Passive rGE
D. CanalizationHeritability estimates for height in the United States are ~.90, but during severe famine they drop drastically. This demonstrates that heritability values are:
A. Fixed across contexts
B. Applicable to individuals
C. Dependent on environmental variability
D. Measures of gene dominanceWhich research design can best disentangle the effects of heredity and environment?
A. Longitudinal case study
B. Cross-sectional survey
C. Monozygotic twin study reared apart
D. Correlational study of siblingsThe term epigenetics refers to:
A. Mutations in DNA sequence
B. Environmental influences turning gene expression on or off
C. Natural selection of advantageous genes
D. Genetic drift across populationsAn introverted adolescent begins volunteering at the library, further reinforcing quiet study habits. This is an example of:
A. Evocative rGE
B. Active rGE
C. Gene flow
D. Cultural transmissionWhich statement about heritability is TRUE?
A. A heritability of .60 means 60 % of your trait is genetic.
B. High heritability implies intervention is useless.
C. Heritability can differ between socioeconomic groups.
D. Heritability estimates are unaffected by measurement error.Identical twins raised together show a personality similarity coefficient of .50; the same twins raised apart show .45. The small difference suggests:
A. Shared environment has a large impact on personality.
B. Non-shared environment drives most personality variance.
C. Genetics play no role in personality.
D. Twin studies are invalid for personality research.Which concept best describes the phenomenon where early childhood stress alters glucocorticoid receptor gene expression, increasing adult vulnerability to anxiety?
A. Critical period plasticity
B. Epigenetic modification
C. Reciprocal altruism
D. Heterozygote advantage
Answer Key
1-B | 2-C | 3-B | 4-C | 5-C | 6-B | 7-B | 8-C | 9-B | 10-B
(Pro tip: Don’t just memorize letters—make sure you can articulate why each distractor is wrong.)
Free-Response Practice
FRQ #1 — Gene–Environment Correlations (7 pts)
Prompt:
Alexandra’s parents are both engineers who love problem-solving games. From infancy, their home is filled with STEM toys and weekly visits to science museums. By middle school, Alexandra eagerly joins robotics club and practices coding on her own. Explain how passive, evocative, and active gene–environment correlations each contribute to Alexandra’s growing aptitude for engineering.
Scoring Guide (sample high-scoring answer bullets):
Passive rGE (1 pt): Parents provide engineering-oriented genes and an enriched STEM environment.
Result (1 pt): Alexandra’s early exposure to puzzles aligns with her inherited spatial reasoning potential.
Evocative rGE (2 pts):
Her evident curiosity elicits more STEM gifts and praise.
Teachers notice her talent, offering advanced math tracks.
Active rGE (2 pts):
She deliberately selects robotics club and coding websites.
These self-chosen settings further hone her engineering skills.
Synthesis (1 pt): Over time, these three correlations spiral, amplifying the initial genetic predisposition into observable expertise.
(Total = 7)
FRQ #2 — Heritability & Reaction Range (7 pts)
Prompt:
Researchers find that heritability of musical pitch discrimination is .70 among students in elite conservatories but only .40 among students in public schools with limited music programs.
a) Interpret what each heritability figure means within its respective group (2 pts).
b) Using reaction range, explain why the estimates differ (2 pts).
c) Describe one environmental intervention likely to narrow the performance gap between groups (1 pt).
d) Explain why a heritability of .70 in conservatories does not imply pitch discrimination cannot be improved through training (2 pts).
Sample High-Scoring Response Outline:
a) Meaning: In conservatories, 70 % of the variance in pitch discrimination among those students is linked to genetic differences; in public schools, it’s 40 %.
b) Reaction Range: Conservatory students share uniformly rich environments, allowing genes to explain more variance; public-school environments are heterogeneous, so environment explains more.
c) Intervention: Provide intensive ear-training curricula and access to quality instruments in public schools.
d) Clarification: Heritability is not destiny; even traits with high h² react to training because genes set bounds, not fixed outcomes. Neural plasticity evidence (musicians’ auditory cortex expansion) shows environment can still push phenotypes upward.
🚀 Exam-Day Flex:
When in doubt, critique the extremes—“All genes” or “all environment” answers are usually traps.
Drop the term “context-dependent” to sound like you own the syllabus.
Nail one killer rGE example (e.g., athletic genes → coaches notice → more playtime) for both MC and FRQ versatility.