MCAT Psychological Social Foundations Flashcards: 7a Behavioral Genetics Gene Environment

What this deck covers

This deck focuses on 7a Behavioral Genetics Gene Environment, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Psychological Social Foundations.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is evocative rGE?

Answer: Genetically influenced traits evoke specific responses from others. Aggressive child elicits harsh discipline; shy child gets protection.

Flashcard 2: What is the shared environment effect ($c^2$) in twin/adoption models?

Answer: Variance due to environmental factors that make siblings similar. Family-wide factors like SES or parenting style affecting all children.

Flashcard 3: What is epigenetics in the study of behavior and psychological traits?

Answer: Heritable gene expression changes without DNA sequence change. Epigenetics involves modifications that alter gene activity and can be passed to offspring without changing the underlying DNA code.

Flashcard 4: What does it mean if $h^2 = 0$ for a trait in a population?

Answer: Observed variance is entirely environmental in that population. A heritability of zero indicates that differences in the trait stem solely from environmental influences within that specific population.

Flashcard 5: What does a high heritability ($h^2$) NOT imply about an individual trait?

Answer: It does not imply genetic determinism or immutability in an individual. Heritability is a population statistic, not an individual measure.

Flashcard 6: What is gene–environment correlation ($rGE$) in behavioral genetics?

Answer: Genetic differences relate to differences in environmental exposure. Gene-environment correlation describes the non-random association between genetic makeup and environmental experiences.

Flashcard 7: State the formula for broad-sense heritability using variance components.

Answer: $h^2=\frac{V_G}{V_P}$. Genetic variance divided by total phenotypic variance.

Flashcard 8: What does it mean if $h^2 = 1$ for a trait in a population?

Answer: Observed variance is entirely genetic in that population. A heritability of one signifies that all variations in the trait are attributable to genetic factors in that population.

Flashcard 9: Identify the genetic relatedness of monozygotic (MZ) twins.

Answer: Approximately $100\%$ of segregating genes shared. Identical twins develop from one zygote, sharing all genes.

Flashcard 10: Which option best defines a gene–environment interaction ($G\times E$)?

Answer: The effect of genes on phenotype depends on the environment (and vice versa). Same genotype produces different phenotypes in different environments.

Flashcard 11: Identify the genetic relatedness of dizygotic (DZ) twins.

Answer: Approximately $50\%$ of segregating genes shared. Fraternal twins develop from two zygotes, like regular siblings.

Flashcard 12: What is passive $rGE$?

Answer: Parents provide both genes and environment correlated with those genes. Child inherits genes that match parent-created environment.

Flashcard 13: What does it mean if $h^2=0$ for a trait in a given population and environment?

Answer: Observed variation is not explained by genetic variation. All trait differences come from environmental factors.

Flashcard 14: Which option best defines gene–environment correlation ($rGE$)?

Answer: Genotypes are associated with particular environments. Genes influence exposure to certain environments.

Flashcard 15: What is shared environment ($C$) in twin/adoption models?

Answer: Environmental influences that make family members more similar. Examples include family SES, parenting style, shared schools.

Flashcard 16: What is the most direct inference when MZ correlations exceed DZ correlations?

Answer: Genetic factors contribute to variance in the trait. Higher correlations in monozygotic twins compared to dizygotic twins indicate that genes play a role in trait differences.

Flashcard 17: What is nonshared environment ($E$) in twin/adoption models?

Answer: Environmental influences that make family members different (plus error). Includes unique experiences, differential treatment, and measurement error.

Flashcard 18: Identify the study design that best separates genetic effects from rearing environment.

Answer: Adoption study. Biological parents provide genes; adoptive parents provide environment.

Flashcard 19: What is the twin study logic for estimating genetic influence on a trait?

Answer: Greater MZ than DZ similarity suggests genetic contribution. MZ twins share more genes, so higher similarity implies genetic influence.

Flashcard 20: What is expressivity in genetics as applied to behavioral traits?

Answer: Degree to which a genotype is expressed in phenotype severity. Expressivity describes the variation in intensity or manifestation of a trait among individuals with the same genotype.

Flashcard 21: What is pleiotropy?

Answer: One gene influences multiple phenotypic traits. Pleiotropy occurs when a single gene affects several distinct traits, contributing to multifaceted genetic influences on behavior.

Flashcard 22: What does it mean if a trait has $h^2=1$?

Answer: All phenotypic variance is explained by genetic variance in that population. All trait variation is due to genetic factors.

Flashcard 23: Which twin type shares about $50\%$ of segregating genes on average?

Answer: Dizygotic twins. Dizygotic twins arise from two separate eggs, sharing approximately half their genetic variants like typical siblings.

Flashcard 24: What is a polygenic trait?

Answer: Trait influenced by many genes, each with small effects. Polygenic traits result from the cumulative effects of numerous genes, explaining complex behavioral variations.

Flashcard 25: What is behavioral genetics?

Answer: Study of genetic and environmental influences on behavior. Examines how genes and environment together shape behaviors.

Flashcard 26: What is heritability ($h^2$) in behavioral genetics?

Answer: Proportion of phenotypic variance due to genetic variance in a population. Measures genetic contribution to trait variation in a population.

Flashcard 27: What is the equal environments assumption in twin studies?

Answer: MZ and DZ twins experience equally similar environments relevant to the trait. Assumes environmental similarity is same for MZ and DZ twins.

Flashcard 28: What is active $rGE$ (niche-picking)?

Answer: Individuals seek environments compatible with their genetic tendencies. People actively select environments matching their genetic predispositions.

Flashcard 29: What is the equal environments assumption in twin studies?

Answer: MZ and DZ twins experience equally similar environments relevant to the trait. Critical assumption for valid heritability estimates from twin comparisons.

Flashcard 30: What is a gene–environment correlation ($rGE$) in behavioral genetics?

Answer: Genetic tendencies influence exposure to particular environments. Genes affect which environments individuals experience.

Flashcard 31: What is dizygotic (DZ) twinning in behavioral genetics research?

Answer: Fraternal twins from two zygotes; share ~50% of segregating DNA. Same genetic similarity as regular siblings but shared prenatal environment.

Flashcard 32: Identify the definition of polygenic inheritance.

Answer: Multiple genes contribute additively to one trait. Many genes each contribute small effects to one trait.

Flashcard 33: What does it mean if a trait has high heritability ($h^2$)?

Answer: Genetic differences explain more variance in that population and context. Genes account for most trait differences in that specific population.

Flashcard 34: What is the key limitation of heritability estimates regarding environments?

Answer: Heritability is environment-specific and can change across environments. Same genes can have different effects in different settings.

Flashcard 35: What is a twin study designed to estimate in behavioral genetics?

Answer: Relative contributions of genes vs environment to trait variation. Twin studies compare similarities between twin types to disentangle genetic and environmental influences on trait variability.

Flashcard 36: State the ACE identity relating variance components to a trait.

Answer: $h^2 + c^2 + e^2 = 1$. All trait variance partitions into genetic, shared, and nonshared components.

Flashcard 37: What is the main purpose of adoption studies in behavioral genetics?

Answer: Separate genetic effects from rearing (shared) environmental effects. Compares adopted children to biological vs. adoptive parents.

Flashcard 38: What is the broad-sense heritability formula in variance terms?

Answer: $h^2 = \frac{V_G}{V_P}$. Broad-sense heritability represents the ratio of genetic variance to total phenotypic variance in a population.

Flashcard 39: Identify the concept: many genes each contribute small effects to a trait.

Answer: Polygenic inheritance. Complex traits result from cumulative effects of multiple genes.

Flashcard 40: What is histone acetylation typically associated with in gene expression?

Answer: Increased transcription (more open chromatin). Histone acetylation relaxes chromatin structure, facilitating access to DNA and enhancing gene transcription rates.

Flashcard 41: What is DNA methylation typically associated with in gene expression?

Answer: Reduced transcription (gene silencing). DNA methylation adds methyl groups to DNA, typically repressing gene expression by inhibiting transcription factors.

Flashcard 42: Which option best describes polygenic inheritance of a behavioral trait?

Answer: Many genes each contribute small additive effects to the phenotype. Complex traits result from cumulative effects of multiple genes.

Flashcard 43: What is a gene–environment correlation (rGE)?

Answer: Genetic differences influence exposure to particular environments. Genes affect which environments individuals experience.

Flashcard 44: What is active rGE (niche-picking)?

Answer: Individuals seek environments that match genetically influenced traits. Extroverts choose social activities; introverts prefer solitary pursuits.

Flashcard 45: What is evocative (reactive) $rGE$?

Answer: Genetically influenced traits elicit specific responses from others. Child's genetic traits trigger specific environmental responses.

Flashcard 46: Which twin type is genetically identical: monozygotic or dizygotic?

Answer: Monozygotic twins. Monozygotic twins develop from a single fertilized egg, sharing 100% of their genetic material.

Flashcard 47: What is phenotype in behavioral genetics?

Answer: Observable trait resulting from genes and environment. Phenotype emerges from the interaction between an individual's genetic composition and environmental influences.

Flashcard 48: State the standard variance-partitioning identity for phenotypes: $V_P = ?$

Answer: $V_P = V_G + V_E + V_{G\times E}$. This equation partitions phenotypic variance into genetic, environmental, and gene-environment interaction components.

Flashcard 49: Compute Falconer heritability given $r_{MZ}=0.80$ and $r_{DZ}=0.50$.

Answer: $h^2=2(r_{MZ}-r_{DZ})=0.60$. Falconer's formula: twice the difference in twin correlations.

Flashcard 50: What is epigenetics in the context of behavior and environment?

Answer: Heritable changes in gene expression without DNA sequence change. Environmental factors alter gene activity without changing DNA code.

Flashcard 51: What is concordance in twin studies?

Answer: Probability that both twins show a trait given that one twin shows it. Measures trait similarity between twin pairs.

Flashcard 52: What is genotype in behavioral genetics?

Answer: An individual's genetic makeup (alleles carried). Genotype refers to the specific combination of alleles an individual inherits, determining potential traits.

Flashcard 53: What is epigenetics in the context of behavior?

Answer: Environment-related changes in gene expression without DNA sequence change. Environmental factors alter gene activity patterns.

Flashcard 54: What is active $rGE$ (niche-picking)?

Answer: Individuals seek environments matching genetic predispositions. Active rGE involves individuals actively selecting or creating environments that align with their genetic tendencies.

Flashcard 55: What is active gene–environment correlation (niche picking)?

Answer: An individual seeks environments consistent with genetic predispositions. People select environments matching their genetic tendencies.

Flashcard 56: What is evocative (reactive) gene–environment correlation?

Answer: An individual's heritable traits evoke specific responses from others. Genetically outgoing children receive more social interaction.

Flashcard 57: State the phenotypic variance decomposition used in basic behavioral genetics.

Answer: $V_P=V_G+V_E+V_{G\times E}$. Total variance equals genetic + environmental + interaction variance.

Flashcard 58: Identify the study design that most directly estimates heritability by comparing MZ vs DZ twins.

Answer: Twin study. MZ twins share 100% genes; DZ twins share 50% on average.

Flashcard 59: What is monozygotic (MZ) twinning in behavioral genetics research?

Answer: Identical twins from one zygote; share ~100% of segregating DNA. Genetically identical twins crucial for parsing genetic vs environmental effects.

Flashcard 60: What is the key limitation of heritability estimates regarding individuals?

Answer: Heritability does not apply to individuals; it applies to populations. Describes variance in groups, not individual trait causation.

Flashcard 61: Identify the key assumption of classical twin studies about environments.

Answer: Equal environments assumption for MZ and DZ twins. The equal environments assumption posits that monozygotic and dizygotic twins experience comparable environmental similarities.

Flashcard 62: What is the polygenic model of complex behavioral traits?

Answer: Many genes of small effect contribute additively to one trait. Complex traits result from cumulative effects of multiple genes.

Flashcard 63: What does it mean if a trait has $h^2=0$?

Answer: Genetic variance does not explain phenotypic variance in that population. All trait variation is due to environmental factors.

Flashcard 64: Identify the definition of pleiotropy.

Answer: One gene influences multiple phenotypic traits. Single gene affects multiple seemingly unrelated traits.

Flashcard 65: What is a gene–environment interaction ($G\times E$)?

Answer: Genetic effects on a trait depend on the environment (and vice versa). Same genotype produces different phenotypes in different environments.

Flashcard 66: What is the nonshared environment effect ($e^2$) in twin/adoption studies?

Answer: Environmental influences that make siblings different (plus measurement error). Unique experiences and random developmental variation.

Flashcard 67: What is passive rGE?

Answer: Parents provide both genes and correlated home environment to child. Musical parents pass genes and instruments/lessons to children.

Flashcard 68: What is passive gene–environment correlation ($rGE$)?

Answer: Parents provide both genes and correlated home environments. Children inherit genes and matching family environments.

Flashcard 69: What is heritability ($h^2$) as used in behavioral genetics?

Answer: Proportion of phenotypic variance due to genetic variance in a population. Measures how much genes contribute to trait differences in a group.

Flashcard 70: Identify the concept: one gene influences multiple phenotypic traits.

Answer: Pleiotropy. Single gene affects multiple seemingly unrelated characteristics.

Flashcard 71: What is heritability ($h^2$) as used in behavioral genetics?

Answer: Proportion of trait variance in a population due to genes. Heritability quantifies the extent to which genetic differences account for observed variations in a trait across individuals in a group.

Flashcard 72: What is passive $rGE$?

Answer: Parents provide both genes and correlated home environment. Passive rGE arises when parental genetics influence both the child's inherited genes and the rearing environment provided.

Flashcard 73: What does it mean if $h^2=1$ for a trait in a given population and environment?

Answer: Observed variation is fully explained by genetic variation. All trait differences come from genetic factors.

Flashcard 74: What is behavioral genetics in the context of psychological traits and behavior?

Answer: Study of genetic and environmental contributions to behavior. Behavioral genetics examines how both hereditary factors and surroundings shape psychological characteristics and actions.

Flashcard 75: State the formula for broad-sense heritability in variance terms.

Answer: $h^2=\frac{V_G}{V_P}$. Genetic variance divided by total phenotypic variance.

Flashcard 76: What is behavioral genetics in the context of MCAT psychology and sociology?

Answer: Study of genetic and environmental influences on behavior. Examines how genes and environment jointly shape behaviors.

Flashcard 77: What is penetrance in genetics as applied to behavioral traits?

Answer: Probability a genotype produces its associated phenotype. Penetrance measures the likelihood that a particular genetic variant will manifest as the expected behavioral or psychological trait.

Flashcard 78: What is the nonshared environment effect ($e^2$) in twin/adoption models?

Answer: Variance due to experiences that make siblings different (plus error). Unique experiences, peer groups, and measurement error create differences.

Flashcard 79: State the formula for broad-sense heritability using variances.

Answer: $h^2=\frac{V_G}{V_P}$. Genetic variance divided by total phenotypic variance.

Flashcard 80: Which twin type is expected to show higher concordance for highly heritable traits: MZ or DZ?

Answer: Monozygotic (MZ) twins. MZ twins share 100% of DNA vs DZ twins' 50%.

Flashcard 81: What is the difference between genotype and phenotype?

Answer: Genotype is genetic makeup; phenotype is expressed trait. Genotype is DNA code; phenotype is observable characteristics.

Flashcard 82: What is heritability ($h^2$) in behavioral genetics?

Answer: Proportion of phenotypic variance due to genetic variance in a population. Measures genetic contribution to trait variation in a population.

Flashcard 83: What is evocative (reactive) gene–environment correlation ($rGE$)?

Answer: An individual elicits environmental responses based on genetically influenced traits. Others respond differently based on person's genetic traits.

Flashcard 84: What is active gene–environment correlation ($rGE$)?

Answer: An individual selects environments consistent with genetic predispositions. People seek environments matching their genetic tendencies.

Flashcard 85: What is behavioral genetics?

Answer: Study of genetic and environmental contributions to behavior. Examines how genes and environment shape behavioral traits.

Flashcard 86: What is passive gene–environment correlation?

Answer: Parents provide both genes and environment correlated with those genes. Musical parents give musical genes and musical home environment.

Flashcard 87: What is evocative (reactive) $rGE$?

Answer: Genetically influenced traits evoke specific responses from others. Evocative rGE occurs as innate genetic traits elicit particular environmental reactions from others, shaping experiences.

Flashcard 88: Identify the correct interpretation of heritability: individual or population level?

Answer: Population level; it does not measure an individual's genetic determination. Describes variance in a population, not individual genetics.

Flashcard 89: What is the shared environment effect ($c^2$) in twin/adoption studies?

Answer: Environmental influences that make siblings more similar. Family environment, parenting, and shared experiences.

Flashcard 90: What is the key limitation of heritability estimates across different environments?

Answer: They are environment- and population-specific; they do not generalize universally. Heritability changes with different environments and populations.

Flashcard 91: What is phenylketonuria (PKU) most commonly used to illustrate in GxE?

Answer: Genetic disorder preventable by diet; environment can block phenotype. Low-phenylalanine diet prevents intellectual disability despite genetic mutation.

Flashcard 92: What is epigenetics in the context of gene expression and behavior?

Answer: Heritable changes in gene expression without changing DNA sequence. Environmental factors modify gene activity without altering DNA.

Flashcard 93: What is gene–environment interaction ($G\times E$)?

Answer: Effect of genes on phenotype depends on environment (and vice versa). Gene-environment interaction highlights how genetic effects on traits are modulated by environmental conditions, and conversely.