AP Psychology: Heredity and Environment (Drill 1)

Question 1. A researcher wants to determine the relative contributions of genetics and upbringing to adult personality. She studies pairs of identical twins who were separated at birth and raised in different households, comparing them to identical twins raised together.

• A) A longitudinal study tracking individuals across the lifespan in this scenario
• B) A correlational study comparing two different populations
• C) A case study examining a single pair of twins in depth
• D) A twin study designed to tease apart genetic and environmental influences ✓

Explanation: This is a classic twin study design, specifically, the twins-reared-apart method, in which identical twins (who share 100% of their DNA) are compared across different environments to estimate heritability. Because the twins are genetically identical but environmentally distinct, similarities between them point toward genetic contributions. This design is distinct from an adoption study, which compares genetically unrelated individuals raised together. (B) is a misconception: while twin studies involve correlations, calling this a study of "two different populations" mischaracterizes the design, the key feature is the genetic relationship between the pairs, not population comparison. (A) is a true-but-irrelevant distractor: longitudinal studies do track people over time, and some twin studies include a longitudinal component, but the defining feature here is the twin methodology, not the time dimension. [Practice 2]

Question 2. Kayla was born with a genetic predisposition to anxiety. Her parents, aware of this, raised her in a calm, structured household and taught her stress-management strategies from an early age. As a teenager, Kayla shows only mild anxiety and copes effectively. Which concept best explains the role that Kayla's upbringing played in shaping her outcome?

• A) The environment modifying the expression of her genetic predisposition ✓
• B) Natural selection acting on her anxiety-related genes
• C) Regression to the mean reducing her trait over time
• D) Epigenetic changes altering gene expression independent of environmental influence

Explanation: Kayla's story illustrates gene-environment interaction: she carried a genetic risk, but her environment, structured parenting and skill-building, buffered the expression of that risk. The correct answer is (A) because her upbringing didn't eliminate the gene; it influenced how the predisposition was expressed in behavior. (B) is wrong because natural selection operates across generations through differential reproduction, not within an individual's lifetime. (D) is a true-but-irrelevant distractor: epigenetic changes do involve modifications to how genes are expressed, but they do not operate independently of environmental influence, in fact, environment is one of the key drivers of epigenetic change, so this choice misapplies the concept in a way that contradicts the scenario. [Practice 1]

Question 3. A behavior geneticist reports the following heritability estimates for three traits in a large adult sample: General intelligence: 0.50 Extraversion: 0.49 Neuroticism: 0.48 A student concludes: "Because heritability is about 50% for each trait, roughly half of any individual's score is determined by genetics." Which of the following best evaluates the student's conclusion?

• A) The conclusion is correct; heritability tells us exactly how much of an individual's trait is genetic.
• B) The conclusion overstates what heritability means; heritability is a population-level statistic, not a statement about individuals. ✓
• C) The conclusion understates genetics' role; heritability always increases as sample size grows.
• D) The conclusion is correct because heritability estimates describe the proportion of each person's trait caused by genes in that population.

Explanation: Heritability estimates describe how much of the variation in a trait across a population can be attributed to genetic differences; they do not tell us what fraction of any one person's score is "from genes." A heritability of 0.50 means roughly half of the observed differences between people in this sample are associated with genetic variation; it says nothing about what produced any specific individual's score. (A) reflects the classic misreading of heritability the question targets. (D) is the more dangerous distractor: it sounds precise and plausible, but it makes the same individual-level error as the student's conclusion, heritability is about variance across people, not proportions within a person. (C) is false: heritability estimates are not a function of sample size and can vary across different populations and environments. [Practice 3]

Question 4. A developmental psychologist wants to study whether children raised in highly stressful home environments show different brain development than children raised in stable homes. She proposes randomly assigning families to either a "high-stress" condition or a "stable" condition for two years. Which of the following is the most significant problem with this proposed study?

• A) The study cannot establish a correlation between environment and brain development.
• B) Home stress level cannot be operationally defined precisely enough for experimental use.
• C) Randomly assigning families to a high-stress condition would be ethically impermissible. ✓
• D) Brain development cannot be measured accurately in children under experimental conditions.

Explanation: The core problem is ethical: a researcher cannot deliberately expose children to harmful conditions such as chronic stress for the purpose of an experiment, even if the scientific question is valuable. This violates the fundamental ethical principle of protecting participants from harm. (A) is incorrect because the design, if it were permissible, would be a true experiment capable of establishing causation, not just correlation. (B) is wrong: stress can be operationally defined and has been measured in many studies; the obstacle here is ethics, not measurement difficulty. (D) is also wrong: brain imaging in children is technically feasible and widely used in developmental research. [Practice 1]

Question 5. Two studies examine the heritability of depression. Study A uses a sample of adult twins living in a diverse range of socioeconomic environments and reports a heritability estimate of 0.37. Study B uses a sample of adult twins who all grew up in middle-class households with similar educational access and reports a heritability estimate of 0.61. Which of the following best explains why the heritability estimate is higher in Study B?

• A) When environmental variation is reduced, genetic differences account for a larger share of the remaining variation in the trait. ✓
• B) Study A's estimate is more reliable because a wider range of environments gives a more accurate estimate.
• C) Study B's participants were more genetically similar to each other than Study A's participants.
• D) Depression is more heritable in middle-class populations because those individuals face fewer environmental triggers within this framework.

Explanation: When environments are highly similar, as in Study B's narrow socioeconomic band, environmental differences contribute less to observed variation in depression, so genetic differences account for a proportionally larger share of the remaining variation. This is why heritability can legitimately differ across studies of the same trait. (C) is a true-but-irrelevant distractor: the twin design within each study controls for genetic similarity between pair members, and nothing in the description supports concluding that Study B's participants are more genetically alike across pairs. (B) contains a defensible claim, wider environmental variation can improve the accuracy of an estimate, but it explains which estimate is more broadly applicable, not why Study B's estimate is numerically higher. (D) confuses environmental triggers for depression with environmental variation as a statistical concept. [Practice 2]