GENE-ENVIRONMENT INTERPLAY PART II
Overview of the Week
Monday: Reading quiz debrief, discussion of Barnes and Beaver (2012) article on gene-environment interplay.
Wednesday: Conclusion of Chapter 3 with a focus on epigenetics.
Friday: Application of biosocial perspectives to peer relationships (Beaver et al., 2008) and parenting (Beaver et al., 2012).
Articles for Wednesday and Friday's classes will be posted after Monday's class. Wednesday's reading is light, so starting an article early is recommended.
No reading quiz this week.
Reading Quiz Debrief
Overall performance on Quiz 2 was very good.
The average completion time for Quiz 2 was shorter than for Quiz 1, suggesting less reliance on notes.
Study Tip: If notes were used, identify questions requiring a refresher to add to study materials for the midterm, which is two weeks away.
No further questions on identifying rGEs (gene-environment correlations) and GxEs (gene-environment interactions) were present. Remember that they can occur simultaneously, a likely exam question.
Feel free to schedule office hours if you have specific questions about the quiz.
Midterm Preparation: No study guides will be provided. Reading quizzes are a good study source but won't cover everything. This week is crucial for compiling study materials.
Diathesis Stress vs. Differential Susceptibility Model
Diathesis Stress Model: This model suggests that the accumulation of 'at-risk' genes and 'at-risk' environments directly increases the likelihood of antisocial phenotypes.
Analogies: 1 + 1 = 2 vs. 3 + 3 = 6, where the effects are additive.
Differential Susceptibility Model: This model posits that genes determine an individual's susceptibility to environmental impacts. Individuals with certain genes are more vulnerable or exhibit more plasticity in specific environments.
Resource-rich environments: Allow for the greatest genetic expression.
Negative environments: Lead to the greatest environmental influence, implying less individual autonomy.
Barnes & Beaver (2012) Abstract: Marriage and Desistance from Criminal Behavior
This paper was not published in a criminology journal initially because its heritability estimations were deemed unappealing by traditional criminology journals.
This research was part of Dr. Barnes's dissertation.
Traditional Criminological Views on Marriage and Desistance
Traditional criminologists (especially social bonding and life-course theorists) generally believe marriage inhibits criminal behavior.
Mechanism: Marriage increases the perceived costs of crime due to bonding with another person and having more to lose. While the motivation to offend may persist, the likelihood of offending decreases when another person could be negatively impacted.
Research Finding: Studies have found that marriage has no effect on arrests for sporadic and high-rate offenders (often categorized as Life-Course Persistent offenders).
Core Hypothesis of the Paper: Active Gene-Environment Correlation (rGE)
Dr. Barnes adopted a "yes…and" approach, acknowledging the importance of the environment (marriage) but highlighting the overlooked genetic associations to marriage and desistance.
Spuriousness Concern: If genetic factors were not controlled in previous research, the observed effect of marriage on desistance might be spurious (i.e., not a direct causal effect).
Hypothesis: An active rGE is present. This means genetic factors influence both the likelihood of marriage and desistance from crime.
Active rGE and Selection into Marriage
Recall Active rGE: Genetic factors influence an individual's selection into particular environments.
Mechanism: Genes do not directly cause marriage or singlehood but code for phenotypes/traits (e.g., personality characteristics, impulsivity, prosociality) that can influence a person's likelihood of entering and maintaining long-term relationships like marriage.
Figure 1. Proposed Relationship Among Marital Status, Desistance, and Genes: This diagram visually represents the hypothesized pathways where "Genes" influence both "Marital Status" and "Desistance," and "Marital Status" also influences "Desistance."
Add Health Sample and Twin Studies
Dataset Used: Add Health dataset, specifically reinterviewed Wave 1 participants six years later when they were between 18-27 years old.
Data Points: Questions pertained to marital status and offending in the past 12 months, compared to Wave 1 data.
Context: The average age of marriage in 2001 (data collection) was 26.9 years for men and 25.1 years for women.
Inclusion of Biologically Related Siblings: The study included twins, half-siblings, and cousins to allow for the calculation of heritability estimates.
Heritability Estimates: These cannot be calculated without biologically related participants.
Study Method if only one person per household: This would be a molecular genetic association study (if genes were measured) or a survey study, but not a behavior genetic study allowing heritability estimates.
Offending Questions
Replicated Questions: The same 12 offending questions asked at Wave I (adolescence) were asked again in adulthood.
Types of Offending: Questions covered property damage, theft (> ext{ }50), breaking and entering, physical fighting, criminal justice contact, and weapon use.
Limitations: The 12 questions do not capture all types of criminal offending and only pertained to behavior in the past 12 months.
The ACE Model
Methodology: Barnes utilized the ACE model (Additive genetic, Common/Shared environmental, and Unique/Nonshared environmental influences) which is an advanced behavior genetic method (typically graduate-level).
Application: The ACE model is run for each biologically related pair. Knowing their biological similarity allows for the estimation of heritability (A), shared environment (C), and nonshared environment (E) on the likelihood of marriage and desistance.
Figure 2 Diagram of the ACE Model: Illustrates the pathways from A, C, and E factors to outcomes for two siblings, showing genetic correlations (e.g., 1.00 for monozygotic twins, .50 for dizygotic twins/full siblings) and shared/nonshared environmental effects.
Results for Heritability on Marriage
Variance Components: The variance components for A, C, and E add up to 100 ext{%}.
Genetic Factors: Accounted for 56 ext{%} of the variance in marriage outcomes.
Nonshared Environment: Accounted for 44 ext{%} of the variance, indicating the role of random and unique life events in marriage.
Results for Heritability on Desistance
Genetic Factors: Accounted for 49 ext{%} of the variance in desistance outcomes.
Nonshared Environment: Accounted for 51 ext{%} of the variance, suggesting significant influence of random and unique life events in desistance.
Active rGE: Since genetic factors influence both marriage (56 ext{%}) and desistance (49 ext{%}) outcomes, there is evidence supporting the presence of an active rGE.
Discussion of Barnes & Beaver (2012)
Do genetic factors influence an individual's likelihood of getting married?
Yes, genetic factors likely influence personality development, which in turn affects the propensity to marry, indicating an rGE.
The nonshared environment is also impactful, aligning with Sampson and Laub's view that environmental events contribute to marriage.
Do genetic factors influence the likelihood of desistance? Is this an rGE?
Yes. Given that genes influence both marriage and desistance, it is plausible that the same underlying genetic factors impact both outcomes.
This finding provides a genetic explanation for why marriage may not lead to desistance for habitual offenders, as observed in previous research.
Testing for Spuriousness: Barnes tested the effect of marriage on desistance both with and without including genetic influence in the model.
Finding: The effect of marriage on desistance remained significant even after controlling for genetic factors, but the effect was substantially weaker.
Implication: Studies that do not account for genetic influences are likely overestimating the environmental effect of marriage on desistance.
Limitations of Barnes & Beaver (2012)
Age Sample: The study exclusively used a sample of younger adults (aged 18-27), limiting generalizability to older individuals.
Definition of Desistance: Desistance was strictly defined as a complete cessation of crime in the past 12 months, potentially overlooking individuals who are merely reducing their offending or whose offending is more sporadic.
Scope of Offending: The study only tapped into a limited set of criminal offending behaviors (12 questions), not covering all forms of deviance.
Marriage as an Indicator: Marriage may not be a perfect indicator of relationship stability (e.g., unhappy marriages, committed non-married relationships).
Divorce Impact: The study did not address how divorce might impact desistance.
Discussion of Heritability of Marriage
The high heritability factor (56 ext{%}) for marriage outcomes might be surprising.
Other adult milestones potentially influenced by genes: Career choice, political affiliation, educational attainment, religious beliefs, propensity for substance use, social network formation, wealth accumulation.
Epigenetics
Upcoming Topic: Epigenetics will conclude Chapter 3.
Negative Connotation: Epigenetics often carries a negative connotation due to historical abuses and misconceptions, such as analogies to "designer babies" or attempts to create "super soldiers."
True Definition: Epigenetics refers to natural processes where the body turns genes on and off. It does not involve changing the underlying DNA sequence.
Cell Specialization: All cells containing DNA (except red blood cells) have identical DNA. Epigenetics explains how different cells specialize (e.g., heart, skin, liver cells) to perform diverse functions.
Recommendation: Start reading one of Friday's articles to avoid reading both on the same night.
Graduate Class Information
CCJ5635 – Biosocial Criminology (Dr. Beaver): Taught every Spring for 20 years, uses the same textbook as this class but with deeper dives and more readings. Next offering: Spring 2026.
CCJ5721 – Role of Stress in Criminology and Criminal Justice Research (Dr. Schwartz): Taught every two years in the Spring. Focuses on stress, includes mass-market nonfiction books and research articles. Next offering: unknown but aims for Spring every two years.
For degree/credit requirements, consult an academic advisor.
What is Epigenetics?
Definition: Epigenetics refers to changes in gene function that do not involve altering the DNA sequence itself. It's about how genes are turned "on" or "off."
Influence: Natural and environmental factors can "switch" genes on and off.
Two Key Mechanisms: DNA methylation and histone acetylation.
Why Epigenetics Has a Negative Connotation
Misconception: Commonly confused with the idea of changing DNA sequences, which is not what epigenetics is.
Confusion with Eugenics: Often mistakenly linked to eugenics, which is the selective reproduction for "desirable" traits.
Ethical Concerns: Epigenetics is not about creating "designer babies" or "super soldiers." It describes natural cellular processes and how the environment can influence them, without the unethical DNA alteration associated with historical experiments (e.g., Mengele's).
Medical Field: Epigenetics research is growing in medicine, but its goal is not to modify DNA in the unethical ways sometimes imagined.
The Naturally Occurring Process of Epigenetics
DNA Uniformity: All cells in the body (except red blood cells) contain the exact same DNA.
Functional Diversity: Despite identical DNA, cells perform different functions (e.g., heart, skin, liver cells) because they use different proteins.
Mechanism: Epigenetics explains how specific genes are turned on or off to produce the proteins necessary for a cell's specialized function.
Epigenome
Definition: Chemical markers located along DNA strands.
Function: These markers act as "gatekeepers" to genes, turning gene activity on or off.
Key Markers: Methyl groups and acetyl groups.
Dynamic Nature: Epigenome markers can change throughout an individual's life in response to different environments and biological milestones (e.g., chronic smoking, alcohol use).
DNA Methylation
Process: Occurs when DNA methyltransferase enzymes attach a methyl group ( ext{CH}_{3}) to a cytosine nucleotide within the promoter region of a gene.
Cytosine: One of the four nucleotide bases in DNA.
Promoter Region: The section of a gene that acts as its on/off switch.
Effect: The presence of a methyl group on the promoter region blocks RNA polymerase from transcribing the gene.
Consequence: No transcription means no translation, which means no protein is produced.
Outcome: DNA methylation typically turns a gene off.
Diagram of DNA Methylation (Figure, Slide 30)
Shows a cytosine nucleotide being converted to 5-methyl-cytosine by DNA methyltransferases.
Illustrates how methyl groups attached to the promoter region prevent gene transcription.
Histone Acetylation
Process: Occurs when acetyltransferase enzymes attach an acetyl group ( ext{COCH}_{3}) to histones.
Histones: Proteins around which DNA is tightly spooled to package it into chromosomes.
Effect: Acetylation loosens the tightly spooled DNA, making the genes more accessible for RNA polymerase transcription.
Outcome: Histone acetylation typically turns a gene on.
Rat Pup Example of Histone Acetylation (Weaver et al., 2004)
Study Design: Investigated the impact of maternal care (licking) on rat pups' stress response.
Attentive Mothers: Rat mothers who frequently licked their pups produced confident adult rats.
Inattentive Mothers: Rat mothers who did not lick their pups produced anxious adult rats.
Mechanism: Maternal licking turns on the glucocorticoid receptor (GR) gene in pups.
GR Gene Function: Produces GR proteins, which help rats cope with stressful environments.
Outcome: More GR proteins lead to lower stress responses.
Biological Equipping: Pups not licked have less GR protein and are biologically less equipped to handle stress.
The Unknowns of Epigenetics Research
Complexity of DNA: Science still lacks a comprehensive understanding of all DNA intricacies.
Knowns: We understand how genes are expressed and the mechanisms of methylation and acetylation for turning genes on/off.
Biggest Breakthrough Needed: The "mystery trigger" – we don't know how certain cells receive the signal to attach acetyl or methyl groups and specialize.
Significance of Breakthrough: Understanding this trigger would be one of the most significant biological science breakthroughs in over 100 years, as it would explain cell specialization.
Research in Medicine
Implications of Knowing the Trigger: If we understood the trigger for cell specialization, we could scientifically direct cells to specialize.
Potential Applications:
Organ Regeneration: Grow new organs from stem cells (e.g., kidney cells), eliminating the need for organ donation.
Cancer Research: Prevent cells from becoming cancerous.
Neuron Replacement: Regenerate damaged neurons.
Optical Cell Regeneration: Restore vision after injury or birth complications.
Global Impact: This knowledge could vastly improve quality of life worldwide, particularly in medicine.
What Are Stem Cells? How Do They Relate to Epigenetics?
Stem Cells: Undifferentiated cells capable of replicating themselves and differentiating into specialized cells (via an unknown process).
Epigenetic Relationship: Stem cells have not yet undergone epigenetic processes; they are not specialized. Epigenetic processes transform a stem cell into a specialized cell through an activation process that is still unknown.
Sources of Stem Cells for Study:
Blastocysts: Embryos (about 150 cells, 5-6 days post-fertilization) acquired from IVF clinics with donor consent, if they are not implanted.
Adult Stem Cells: Found in bone marrow (more difficult to use).
Amniotic Fluid/Umbilical Cord Blood: Other sources.
Differentiation: Once a cell becomes specialized (through epigenetics), it is no longer a stem cell.
Why Epigenetics Is Considered a Form of Gene-Environment Interplay
Definition of Gene-Environment Interplay: When genetic influences and environmental factors combine to manifest different phenotypes/traits.
Epigenetics' Role: While epigenetics does not change DNA sequences, it does change phenotypes (e.g., a rat pup's stress response).
Environmental Influence: The environment directly influences epigenetic processes, which, in turn, affect phenotypes (e.g., maternal licking affecting gene expression).
Current State of Research: The full potential understanding of epigenetic research and environmental influences on DNA is still developing.
Ethical Considerations: Human experimentation is limited by ethical concerns, unlike animal studies.
Future Questions: The impact of environmental factors like stress, cigarette smoke, alcohol, drugs, or abuse on epigenetic processes is still being investigated.
For Friday's Class: Peers and Parenting rGE Research
Two articles focusing on gene-environment correlations (rGEs) will be covered.
Beaver et al. (2008): "Delinquent Peer Formation rGE."
This article explores the selection into delinquent peer groups from an rGE perspective.
Differs from previous readings on GxE for peer influence on victimization.
Beaver et al. (2012): "Parental Negativity and Childhood Maltreatment rGE Study."
Examines the influence of DRD2, DRD4, and DAT1 genes on family environment measures.
Delinquent Peer Formation: Evidence of an rGE (Beaver et al., 2008)
Dataset: Also used the Add Health dataset.
Focus: Explores deviant peers through an rGE perspective, focusing on the selection into deviant peer groups, contrasting with a previous GxE article on peer victimization.
Traditional Criminology and Peers
Key Topic: Peers are one of the most extensively studied topics in criminology.
Differential Association Theory (Akers): Delinquent peers transmit antisocial values and behaviors directly to their associates (the "bad influence" idea).
Control Theory (Gottfredson and Hirschi): Hypothesizes that crime-producing traits lead youths to select into antisocial peer networks. While they agree traits influence selection, they disagree that these traits are genetically influenced.
Active rGE for the Current Study
Hypothesis: The study assesses whether the 10R allele of the dopamine transporter gene (DAT1) is associated with self-reported delinquent peer affiliation, indicating an active rGE.
Active rGE Reminder: Genetic factors influence an individual's choice of environment. People choose peer groups that align with their genetic expressions/predispositions (e.g., personality traits).
DAT1 Gene and Peer Group Selection
Previous Research: The 10R allele of the DAT1 gene has been linked to phenotypes such as ADHD, pathological gambling, generalized anxiety disorder, depression, and externalizing behavior in young children.
Study Hypothesis: Beaver et al. hypothesized that these traits, influenced by the DAT1 gene, would correlate with selecting into deviant peer groups. This was the first study to investigate an active rGE between DAT1 and antisocial peer formations.
Methods: Add Health (Again)
Sample: Wave 1 participants, aged 11-19 years.
Measuring Delinquent Peers: Respondents identified if any of their three closest friends engaged in specific behaviors:
Smoking at least one cigarette/day.
Drinking alcohol at least once/month.
Smoking pot at least once/month.
Critique of Measurement: This operationalization of "delinquent peers" is limited to substance use and may not capture all forms of delinquency.
Results: Age and DAT1
Age: The strongest predictor of associating with delinquent peers was age. As age increased, so did association with delinquent peers.
Explanation: Age is both an environmental and biological variable (e.g., puberty related biological changes) and allows for different environmental exposures (e.g., 11-year-olds vs. 17-year-olds in terms of driving, parties, parental monitoring).
DAT1 Results: The 10R allele of the DAT1 gene predicted having antisocial friends, but only for males.
Possible Reasons for Sex-Specificity: Male delinquent groups might be more common, or female delinquency may manifest in ways not captured by the survey questions.
Risk Alleles: Males with a greater number of risk alleles were more likely to be involved with delinquent peers.
Evidence of rGE: Confirms that individuals with specific genotypes are more prone to seeking environments aligning with their genetic predispositions.
Different Models for Different Family Environments
Beaver and colleagues ran an additional model to examine if the DAT1 results held true across different family environments.
Finding: The effect of the DAT1 allele on delinquent peer formation for males was dependent on the family environment.
Interaction: The DAT1 allele's effect on delinquent peer formation was significant only for males residing in an at-risk family environment.
Connection: This finding resembles the "differential susceptibility" or GxE interaction models, where genetic predisposition is expressed only under specific environmental conditions.
Likely a Simultaneous GxE and rGE
Previous Connection: Similar to the "deviant peers x DRD2 gene" article, where DRD2 affected victimization only for White males with few/no delinquent peers.
Current Study Illustration: Males with an at-risk genotype (DAT1 10R allele) are more likely to seek out deviant peers, but only if they are also in an at-risk family environment.
Conclusion: Both studies suggest that genes and environmental influences interact in both the selection into peer groups (rGE) and the subsequent outcomes within those groups (GxE).
What Can Explain These Findings?
Parental Role: For males with the DAT1 10R allele, the effect on associating with delinquent peers was only significant in at-risk family environments.
Mitigation: More involved and attached parents might mitigate genetic tendencies through stricter monitoring and curfews.
rGE Influence: Genetic predisposition influences the likelihood of selecting into delinquent peer groups when an at-risk environment is already present.
GxE Influence: The interaction of genes and environment influences the likelihood of antisocial outcomes after an individual has selected into a peer group.
Study Limitations of Beaver et al. (2008)
Definition of Delinquent Peers: Limited to substance use, excluding more serious law-breaking or other delinquent behaviors.
Sample Size for Genotyping: Only a small subsample of Add Health participants was genotyped, ideally requiring a larger sample for stronger inference.
At-Risk Family Environment Measurement: Defined solely by maternal attachment and involvement, self-reported by adolescents, which may not encompass all aspects of "at-risk" family environments.
Gene Influences on Measures of Parental Negativity & Childhood Maltreatment (Beaver et al., 2012)
Abstract: This study investigates the effect of multiple genes (DRD2, DRD4, DAT1) on multiple outcomes: maternal negativity, paternal negativity, and childhood maltreatment.
Important Note: Only the children were genotyped, and parent measures were self-reported by the children/adolescents.
Parents – Apparently, It's All Their Fault
Common Blame: When children misbehave, parents are often the first to be questioned.
Traditional Criminology View: Parenting is seen as a purely environmental process. The way parents socialize (or fail to socialize) their children directly "molds" offspring outcomes (e.g., ineffective parenting $
ightarrow$ adolescent delinquency).Missing Link: Traditional criminology often overlooks what predicts ineffective parenting itself.
Behavioral Genetic Research on Parenting
Plomin et al. (1994): Studied heritability for 18 family measures.
Finding: 15 of these family measures were influenced by genetic factors.
Heritability Estimate: Approximately 26 ext{%} of the variance in the family environment was attributable to genetic factors.
Significance: While 26 ext{%} might seem small, it is not insignificant. It demonstrates that the environment does not account for 100 ext{%}$$ of the variance in parenting measures, and genetic influences play a role.
Current Study – Looks at Multiple Dopamine Genes
Hypothesis: Genes from the dopaminergic system are hypothesized to be associated with variations in family environments.
Family Environment Outcomes: Maternal negativity, paternal negativity, and childhood maltreatment.
Genetic Alleles Studied: DRD2, DRD4, and DAT1.
How Was Parenting Measured?
Maternal Negativity: Measured emotional attachment and involvement between mother and child (self-reported by child).
Paternal Negativity: Measured emotional attachment and involvement between father and child (self-reported by child).
Childhood Maltreatment: Respondents were asked if they experienced any of the following before 6th grade, by one or both parents:
Left at home alone.
Not provided basic needs (food, clothing, school transport).
Hit, kicked, or slapped.
Touched in a sexual way.
More Genes Studied = More Complex Results
Dopaminergic System: While all genes studied were dopaminergic, their influence on parenting outcomes varied.
DRD2 and DAT1 Findings: Associated with variations in parenting outcomes only for White males.
DRD2: Associated with negative maternal parenting, negative paternal parenting, and childhood maltreatment.
DAT1: Related to variation in maternal parenting only.
DRD4 Findings: Not related to any variation in parenting outcomes in this study.
Is an rGE Present in the Current Study?
Presence of rGE: Yes, based on the study design and findings of genetic influences on parenting outcomes.
Type of rGE (Undifferentiated): The specific type of rGE (evocative, passive, active) cannot be definitively determined from the available data.
Evocative rGE: Do children with certain genetic predispositions elicit specific responses from their parents?
Passive rGE: Do parents transmit genetic predispositions to children along with the environment they provide?
Likely Combination: It is most likely a combination of these types, but differentiation is not possible with the current data structure (e.g., not genotyping parents).
Limitations of the Current Study
Genetic Scope: Hundreds of genes influence the dopaminergic system; it's unclear how many other genes might be influential in parenting outcomes.
Reporting Bias: Parenting outcomes were based on self-reports from adolescents, and only children were genotyped (parents were not).
Replication Concerns: As the first study to assess dopaminergic genes on these specific parenting outcomes, the generalizability and replicability of the results are yet to be confirmed.
Reminders for Next Week
Monday: Review day for Gene-Environment Interplay. Submit questions to Canvas by Saturday noon (or via anonymous email) for slide preparation.
Wednesday: Apply biosocial perspectives to Social Learning Theory (article to be posted).
Friday: Discussion Roundtable on the first half of the class. Bring discussion questions. Attendance is mandatory and will be based on participation.
Next Friday: Final reading quiz before the midterm.
Office hours are available next week for questions or catching up.