Behavioral Genetics and Gene–Environment Interaction (7A) - Psych & Soc

What is evocative rGE?

Genetically influenced traits evoke specific responses from others. Aggressive child elicits harsh discipline; shy child gets protection.
What is the shared environment effect ( $c^2$ ) in twin/adoption models?

Variance due to environmental factors that make siblings similar. Family-wide factors like SES or parenting style affecting all children.
What is epigenetics in the study of behavior and psychological traits?

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

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

It does not imply genetic determinism or immutability in an individual. Heritability is a population statistic, not an individual measure.
What is gene–environment correlation ( $rGE$ ) in behavioral genetics?

Genetic differences relate to differences in environmental exposure. Gene-environment correlation describes the non-random association between genetic makeup and environmental experiences.
State the formula for broad-sense heritability using variance components.

$h^2=\frac{V_G}{V_P}$ . Genetic variance divided by total phenotypic variance.
What does it mean if $h^2 = 1$ for a trait in a population?

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.
Identify the genetic relatedness of monozygotic (MZ) twins.

Approximately $100\%$ of segregating genes shared. Identical twins develop from one zygote, sharing all genes.
Which option best defines a gene–environment interaction ( $G\times E$ )?

The effect of genes on phenotype depends on the environment (and vice versa). Same genotype produces different phenotypes in different environments.
Identify the genetic relatedness of dizygotic (DZ) twins.

Approximately $50\%$ of segregating genes shared. Fraternal twins develop from two zygotes, like regular siblings.
What is passive $rGE$ ?

Parents provide both genes and environment correlated with those genes. Child inherits genes that match parent-created environment.
What does it mean if $h^2=0$ for a trait in a given population and environment?

Observed variation is not explained by genetic variation. All trait differences come from environmental factors.
Which option best defines gene–environment correlation ( $rGE$ )?

Genotypes are associated with particular environments. Genes influence exposure to certain environments.
What is shared environment ( $C$ ) in twin/adoption models?

Environmental influences that make family members more similar. Examples include family SES, parenting style, shared schools.
What is the most direct inference when MZ correlations exceed DZ correlations?

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.
What is nonshared environment ( $E$ ) in twin/adoption models?

Environmental influences that make family members different (plus error). Includes unique experiences, differential treatment, and measurement error.
Identify the study design that best separates genetic effects from rearing environment.

Adoption study. Biological parents provide genes; adoptive parents provide environment.
What is the twin study logic for estimating genetic influence on a trait?

Greater MZ than DZ similarity suggests genetic contribution. MZ twins share more genes, so higher similarity implies genetic influence.
What is expressivity in genetics as applied to behavioral traits?

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.
What is pleiotropy?

One gene influences multiple phenotypic traits. Pleiotropy occurs when a single gene affects several distinct traits, contributing to multifaceted genetic influences on behavior.
What does it mean if a trait has $h^2=1$ ?

All phenotypic variance is explained by genetic variance in that population. All trait variation is due to genetic factors.
Which twin type shares about $50\%$ of segregating genes on average?

Dizygotic twins. Dizygotic twins arise from two separate eggs, sharing approximately half their genetic variants like typical siblings.
What is a polygenic trait?

Trait influenced by many genes, each with small effects. Polygenic traits result from the cumulative effects of numerous genes, explaining complex behavioral variations.
What is behavioral genetics?

Study of genetic and environmental influences on behavior. Examines how genes and environment together shape behaviors.
What is heritability ( $h^2$ ) in behavioral genetics?

Proportion of phenotypic variance due to genetic variance in a population. Measures genetic contribution to trait variation in a population.
What is the equal environments assumption in twin studies?

MZ and DZ twins experience equally similar environments relevant to the trait. Assumes environmental similarity is same for MZ and DZ twins.
What is active $rGE$ (niche-picking)?

Individuals seek environments compatible with their genetic tendencies. People actively select environments matching their genetic predispositions.
What is the equal environments assumption in twin studies?

MZ and DZ twins experience equally similar environments relevant to the trait. Critical assumption for valid heritability estimates from twin comparisons.
What is a gene–environment correlation ( $rGE$ ) in behavioral genetics?

Genetic tendencies influence exposure to particular environments. Genes affect which environments individuals experience.
What is dizygotic (DZ) twinning in behavioral genetics research?

Fraternal twins from two zygotes; share ~50% of segregating DNA. Same genetic similarity as regular siblings but shared prenatal environment.
Identify the definition of polygenic inheritance.

Multiple genes contribute additively to one trait. Many genes each contribute small effects to one trait.
What does it mean if a trait has high heritability ( $h^2$ )?

Genetic differences explain more variance in that population and context. Genes account for most trait differences in that specific population.
What is the key limitation of heritability estimates regarding environments?

Heritability is environment-specific and can change across environments. Same genes can have different effects in different settings.
What is a twin study designed to estimate in behavioral genetics?

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.
State the ACE identity relating variance components to a trait.

$h^2 + c^2 + e^2 = 1$ . All trait variance partitions into genetic, shared, and nonshared components.
What is the main purpose of adoption studies in behavioral genetics?

Separate genetic effects from rearing (shared) environmental effects. Compares adopted children to biological vs. adoptive parents.
What is the broad-sense heritability formula in variance terms?

$h^2 = \frac{V_G}{V_P}$ . Broad-sense heritability represents the ratio of genetic variance to total phenotypic variance in a population.
Identify the concept: many genes each contribute small effects to a trait.

Polygenic inheritance. Complex traits result from cumulative effects of multiple genes.
What is histone acetylation typically associated with in gene expression?

Increased transcription (more open chromatin). Histone acetylation relaxes chromatin structure, facilitating access to DNA and enhancing gene transcription rates.
What is DNA methylation typically associated with in gene expression?

Reduced transcription (gene silencing). DNA methylation adds methyl groups to DNA, typically repressing gene expression by inhibiting transcription factors.
Which option best describes polygenic inheritance of a behavioral trait?

Many genes each contribute small additive effects to the phenotype. Complex traits result from cumulative effects of multiple genes.
What is a gene–environment correlation (rGE)?

Genetic differences influence exposure to particular environments. Genes affect which environments individuals experience.
What is active rGE (niche-picking)?

Individuals seek environments that match genetically influenced traits. Extroverts choose social activities; introverts prefer solitary pursuits.
What is evocative (reactive) $rGE$ ?

Genetically influenced traits elicit specific responses from others. Child's genetic traits trigger specific environmental responses.
Which twin type is genetically identical: monozygotic or dizygotic?

Monozygotic twins. Monozygotic twins develop from a single fertilized egg, sharing 100% of their genetic material.
What is phenotype in behavioral genetics?

Observable trait resulting from genes and environment. Phenotype emerges from the interaction between an individual's genetic composition and environmental influences.
State the standard variance-partitioning identity for phenotypes: $V_P = ?$

$V_P = V_G + V_E + V_{G\times E}$ . This equation partitions phenotypic variance into genetic, environmental, and gene-environment interaction components.
Compute Falconer heritability given $r_{MZ}=0.80$ and $r_{DZ}=0.50$ .

$h^2=2(r_{MZ}-r_{DZ})=0.60$ . Falconer's formula: twice the difference in twin correlations.
What is epigenetics in the context of behavior and environment?

Heritable changes in gene expression without DNA sequence change. Environmental factors alter gene activity without changing DNA code.
What is concordance in twin studies?

Probability that both twins show a trait given that one twin shows it. Measures trait similarity between twin pairs.
What is genotype in behavioral genetics?

An individual's genetic makeup (alleles carried). Genotype refers to the specific combination of alleles an individual inherits, determining potential traits.
What is epigenetics in the context of behavior?

Environment-related changes in gene expression without DNA sequence change. Environmental factors alter gene activity patterns.
What is active $rGE$ (niche-picking)?

Individuals seek environments matching genetic predispositions. Active rGE involves individuals actively selecting or creating environments that align with their genetic tendencies.
What is active gene–environment correlation (niche picking)?

An individual seeks environments consistent with genetic predispositions. People select environments matching their genetic tendencies.
What is evocative (reactive) gene–environment correlation?

An individual's heritable traits evoke specific responses from others. Genetically outgoing children receive more social interaction.
State the phenotypic variance decomposition used in basic behavioral genetics.

$V_P=V_G+V_E+V_{G\times E}$ . Total variance equals genetic + environmental + interaction variance.
Identify the study design that most directly estimates heritability by comparing MZ vs DZ twins.

Twin study. MZ twins share 100% genes; DZ twins share 50% on average.
What is monozygotic (MZ) twinning in behavioral genetics research?

Identical twins from one zygote; share ~100% of segregating DNA. Genetically identical twins crucial for parsing genetic vs environmental effects.
What is the key limitation of heritability estimates regarding individuals?

Heritability does not apply to individuals; it applies to populations. Describes variance in groups, not individual trait causation.
Identify the key assumption of classical twin studies about environments.

Equal environments assumption for MZ and DZ twins. The equal environments assumption posits that monozygotic and dizygotic twins experience comparable environmental similarities.
What is the polygenic model of complex behavioral traits?

Many genes of small effect contribute additively to one trait. Complex traits result from cumulative effects of multiple genes.
What does it mean if a trait has $h^2=0$ ?

Genetic variance does not explain phenotypic variance in that population. All trait variation is due to environmental factors.
Identify the definition of pleiotropy.

One gene influences multiple phenotypic traits. Single gene affects multiple seemingly unrelated traits.
What is a gene–environment interaction ( $G\times E$ )?

Genetic effects on a trait depend on the environment (and vice versa). Same genotype produces different phenotypes in different environments.
What is the nonshared environment effect ( $e^2$ ) in twin/adoption studies?

Environmental influences that make siblings different (plus measurement error). Unique experiences and random developmental variation.
What is passive rGE?

Parents provide both genes and correlated home environment to child. Musical parents pass genes and instruments/lessons to children.
What is passive gene–environment correlation ( $rGE$ )?

Parents provide both genes and correlated home environments. Children inherit genes and matching family environments.
What is heritability ( $h^2$ ) as used in behavioral genetics?

Proportion of phenotypic variance due to genetic variance in a population. Measures how much genes contribute to trait differences in a group.
Identify the concept: one gene influences multiple phenotypic traits.

Pleiotropy. Single gene affects multiple seemingly unrelated characteristics.
What is heritability ( $h^2$ ) as used in behavioral genetics?

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.
What is passive $rGE$ ?

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

Observed variation is fully explained by genetic variation. All trait differences come from genetic factors.
What is behavioral genetics in the context of psychological traits and behavior?

Study of genetic and environmental contributions to behavior. Behavioral genetics examines how both hereditary factors and surroundings shape psychological characteristics and actions.
State the formula for broad-sense heritability in variance terms.

$h^2=\frac{V_G}{V_P}$ . Genetic variance divided by total phenotypic variance.
What is behavioral genetics in the context of MCAT psychology and sociology?

Study of genetic and environmental influences on behavior. Examines how genes and environment jointly shape behaviors.
What is penetrance in genetics as applied to behavioral traits?

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

Variance due to experiences that make siblings different (plus error). Unique experiences, peer groups, and measurement error create differences.
State the formula for broad-sense heritability using variances.

$h^2=\frac{V_G}{V_P}$ . Genetic variance divided by total phenotypic variance.
Which twin type is expected to show higher concordance for highly heritable traits: MZ or DZ?

Monozygotic (MZ) twins. MZ twins share 100% of DNA vs DZ twins' 50%.
What is the difference between genotype and phenotype?

Genotype is genetic makeup; phenotype is expressed trait. Genotype is DNA code; phenotype is observable characteristics.
What is heritability ( $h^2$ ) in behavioral genetics?

Proportion of phenotypic variance due to genetic variance in a population. Measures genetic contribution to trait variation in a population.
What is evocative (reactive) gene–environment correlation ( $rGE$ )?

An individual elicits environmental responses based on genetically influenced traits. Others respond differently based on person's genetic traits.
What is active gene–environment correlation ( $rGE$ )?

An individual selects environments consistent with genetic predispositions. People seek environments matching their genetic tendencies.
What is behavioral genetics?

Study of genetic and environmental contributions to behavior. Examines how genes and environment shape behavioral traits.
What is passive gene–environment correlation?

Parents provide both genes and environment correlated with those genes. Musical parents give musical genes and musical home environment.
What is evocative (reactive) $rGE$ ?

Genetically influenced traits evoke specific responses from others. Evocative rGE occurs as innate genetic traits elicit particular environmental reactions from others, shaping experiences.
Identify the correct interpretation of heritability: individual or population level?

Population level; it does not measure an individual's genetic determination. Describes variance in a population, not individual genetics.
What is the shared environment effect ( $c^2$ ) in twin/adoption studies?

Environmental influences that make siblings more similar. Family environment, parenting, and shared experiences.
What is the key limitation of heritability estimates across different environments?

They are environment- and population-specific; they do not generalize universally. Heritability changes with different environments and populations.
What is phenylketonuria (PKU) most commonly used to illustrate in GxE?

Genetic disorder preventable by diet; environment can block phenotype. Low-phenylalanine diet prevents intellectual disability despite genetic mutation.
What is epigenetics in the context of gene expression and behavior?

Heritable changes in gene expression without changing DNA sequence. Environmental factors modify gene activity without altering DNA.
What is gene–environment interaction ( $G\times E$ )?

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.

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