Genetics and Personality 2

• Behavioural Genetics Studies


  • Look for observable differences and similarities in personality using observation, interviews, and/or self-rating scales
  • Explore and identify genetic and environmental contributions
• Main types of behavioural genetics studies

  • Family (Linkage)
  • Twin
  • Adoption
  • Association
• Family (Linkage) Studies


  1. Track traits & genes through families

  2. Assess proportion of each that are shared

  3. Impacted by mode of inheritance

  4. Large environmental influence, limited insights

  
• DISC1


  A completely novel gene that makes a completely novel protein, each of unknown function
• DISC1 pathway


  • Modulates expression of neurodevelopment, synaptic and sensory perception genes
• Family (Linkage) Studies on DISC1

  1. Assessed 54 members of a single family spanning 5 generations

  2. 36 with no known history, and 18 members with known history of major mental illness

  3. Looked for genetic features common to all cases of mental illness in the family

  4. Identified genome-wide significant linkage scores

  5. Showed impact of dominant v recessive inheritance

  6. Variable penetrance (proportion of people with that gene variant that express associated trait)

  7. DISC gene more related to broad diagnosis (e.g., major mental illness)

  
• Twin & Multiple Birth Studies


  Allow us to better assess the absolute and relative importance of environmental and genetic influences

  
• Traits of identical twins raised in the same environment rarely show 100% correlation
• Trait A


  Higher shared environmental variance, low heritability
• Trait B


  Higher correlation with genetic similarity, high heritability
• Trait C


  Low sibling correlation, low heritability
• Heritability estimates


  Can be calculated using Falconer's formula: h2 = 2 (rMZ - rDZ)
• Heritability estimates can result in over estimation of heritability
• Limitation of twin studies: Twins share the same environment, but experience of the family may differ
• Adoption Studies


  • Allow us to separate out environment
  • Investigate similarities between adoptees and their biological and adoptive parents
• Correlation in adoption studies provide evidence of genetic influence on Extraversion and Neuroticism, but not Openness
• Association Studies


  • Similar to linkage studies, but assess individuals belonging to a particular population or sample
  • Grouped by shared phenotype, instead of shared genotype
• Impulsivity


  • Short form (S) in chromosome 17 at 17q11.1-q12 decreases re-uptake of 5HT (serotonin)
  • Leads to enhanced processing of aversive or negative cues from the environment, bias to negative information and higher neuroticism scores
  • Possible association with caution?
• Nomura et al. 2015 study on impulsivity

  1. Assessed specific 5HTTLPR genotypes using a Go/NoGo punishment feedback task (motor impulsivity)

  2. Errors: Commissions (NoGo responses), Omissions (missed Go responses)

  3. Addition of a reward component used to tweak consequences of errors

  4. s/s group made fewer commission errors when NoGo errors were being punished

  5. 5HT (s/s) genotype had more effect on responding when the consequences of not withholding a response was high

  6. Cautious people (s/s carriers) become even more cautious when they are likely to be punished

  7. Link may be through the evaluation of potential risk
• Studies on 5HT transporter and Substance Use

  • Wang et al. 2011 assessed the Yunnan Han population: l/l and l/s genotype was significantly lower in alcohol dependence than control group
  • Merenakk et al. 2011 assessed Estonian children and adolescents: Substance use did not differ by genotype at age 9, but people with the short (s/s) genotype had higher tobacco use at age 15 and were more active alcohol, drug and tobacco users at age 18
• Studies suggest that the 5HT (s/s) genotype is impacting impulsivity, and those with this genotype are more likely to be impulsive and use substances
• Important considerations in behavioural genetics

  • Additive genetic variance
  • Dominant genetic variance (likelihood of genes expressed)
  • Epistatic genetic variance (interaction)
  • Epigenetic variance (environment changes gene expression, e.g. famine and physical disorders like diabetes, obesity)
  • Operationalisation of phenotypes (how are we defining and measuring our phenotypes?)