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Genetics and Personality Slides

Genetics and Personality

  • Author: Emma Barkus

Objectives

  • Appreciate the different approaches to genetic studies:

    • Heritability estimates

    • Twin studies

    • Linkage studies

    • Association studies

  • Outline existing research in genetics and personality.

Heritability Estimates

  • Definition: Percentage of variance explained by genes

  • Environment and genes must equal 100%. For instance, if 60% is genetic, 40% is environmental.

  • Expressed as a percentage or correlation.

GREML and Big-5 Personality Traits

  • GREML analysis explores how small genetic variations (SNPs) relate to outcomes.

  • Example study (Vinkhuyzen et al., 2012) with 12,000 unrelated individuals found:

    • 6% variance in neuroticism

    • 12% variance in extraversion

  • Verweij et al. (2012) on 8000 individuals found:

    • 7% for harm avoidance

    • 10% for novelty seeking

    • 8% for persistence

  • Suggests a general factor of personality could exist based on genetic overlap.

Power and Pluess (2015) Study

  • Sample from 1958 National Child Development Study:

    • Included 4855-4924 individuals in analysis.

  • Participants completed the IPIP Big-5 questionnaire at age 50.

  • Findings on heritability estimates include:

    • Openness to Experience: 21%

    • Neuroticism: 15%

    • No significant findings on other traits.

  • Noted genetic overlap between Neuroticism and Openness.

Conclusions from Power and Pluess (2015)

  • Approximately 25% of genetic variability in neuroticism and openness is attributed to common, small genetic variants.

  • Evidence indicates a heritable general personality factor.

  • Some aspects of personality are moderately heritable, though the specifics (general vs specific traits) remain unclear.

Twin Studies

  • Found that 40-60% of variance in the Big-5 traits is heritable.

  • Monozygotic twins share the same environment in the womb and family:

    • However, family experiences differ for individuals.

    • External experiences become influential as children age.

  • Twin correlation calculation:

    • Monozygotic - Dizygotic correlations are doubled and expressed as a percentage.

Genetic Variance Shared

  • Monozygotic twins share ~100% of genetic variance.

  • Dizygotic twins share 50% of genetic variance.

  • Siblings also share 50% genetic variance.

Riemann, Angleitner, & Strelau (1997) Study

  • Screened over 1000 twins (660 monozygotic, 200 same-sex dizygotic, 104 opposite-sex dizygotic).

  • No significant differences in age, education, or occupational status between MZ and DZ twins.

Main Results: Table on Twin Correlations

  • Neuroticism: MZ .53 | DZ .60

  • Extraversion: MZ .56 | DZ .59

  • Openness: MZ .54 | DZ .55

  • Agreeableness: MZ .42 | DZ .49

  • Conscientiousness: MZ .54 | DZ .52

  • Mean correlations: MZ .52 | DZ .55

  • All statistics corrected for age and sex effects.

Adoption Studies

  • Allow for distinguishing between genetic and environmental influences.

  • Investigate closeness of relationship with adopted vs biological parents.

Correlations in Personality Variables

  • Comparison of identical twins reared together, separated, fraternal twins together, and separated.

Summary of Twin and Adoption Studies

  • Evidence suggests genetic elements in personality exist.

  • However, significant variance is still attributed to environmental factors.

Linkage Studies

  • Investigates sections of chromosomes associated with specific traits (phenotypes).

  • Understand trait inheritance through generations, and assess gender presence.

  • Typically identifies chromosomal regions but requires additional analysis for specificity.

High NEO Personality Traits: Amin et al. (2012)

  • From Erasmus Rucphen Family study, involving 2657 individuals from a genetically isolated area of the Netherlands.

  • Analyzed traits: Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism (top 10% affected).

Amin et al. (2012) Linkage Findings

  • Conscientiousness linked to 20p13, Neuroticism to 19q, 21q, 22q.

  • Extraversion linked to 1p, 1q, 9p, 12q.

  • Openness to 12q and 19q; Agreeableness to 2p, 6q, 17q, 21q.

  • Links show overlap in chromosomal regions mirroring trait correlations.

Amin et al. Results Summary

  • Linkage analysis showed no single gene exerting a large effect on personality.

  • Identified regions associated with personality traits are often linked to disorders (e.g., Down’s Syndrome).

Association Studies: Impulsivity

  • Impulsivity linked to marker 17q11.1-q12.

  • Short form (S) decreases re-uptake of serotonin, correlates with higher neuroticism scores.

  • Suggests S form may promote cautious behavior.

Association Studies: Nomura et al. (2015)

  • Studied specific 5-HTTLPR genotypes in Japanese volunteers, focusing on motor impulsivity via Go/Nogo feedback.

Experimental Design Details

  • Task involved Go/Nogo stimuli to assess impulse control.

  • Randomized inter-stimulus intervals.

Error Types in Response Tasks

  • Commission: Responding inaccurately.

  • Omission: Failing to respond appropriately.

  • Modification of tasks included a reward component for error responses.

5HT Transporter, Impulsivity, and Genetic Influence

  • Measured via Go/No Go tasks; s/s carriers showed fewer commission errors when punished.

  • Indicates 5-HT genotype influences cautious behavior under threat of punishment.

Challenges in Genetic Studies

  • Different types of genetic variance (additive, dominant, epistatic, epigenetic).

  • Environmental impacts on gene expression (e.g., famine affecting health disorders).

  • Phenotype definitions vary, complicating studies.

Genes, Environment, and Personality

  • Genes influence cell structure and function; environment influences organs (e.g., brain) and behavior (phenotype).

Key References

  • Bouchard TJ Jr, McGue M. (2003).

  • Jang KL et al. (1996).

  • Nomura et al. (2015).

  • Riemann et al. (1997).

  • Vernon PA et al. (2008).

  • Verweij et al. (2012).

  • Vinkhuyzen et al. (2012).