Gene-Environment Interactions

• Gene-environment interactions


  • The environment can influence whether genetic information is expressed (switch ON/OFF) and how it is expressed (gene activity level)
  • An environmental/genetic trigger can lead to a cascade of subsequent genetic and environmental changes

  
• Canalisation


  • (Epi-) genetic restriction to a small number of developmental outcomes
  • Increased cell specialisation through epigenetic regulation

  
• Epigenetic regulation

  • Epigenetics = ‘on top of genetics’; ‘on top of DNA code’
  • Prof Jonathan Mill: If you think of DNA as the hardware, then the epigenome is the software, regulating how DNA is utilised in different cells and at different times
  • Epigenetic regulation often involves methylation
  • Regulation is often precisely timed, ensuring change happens in right developmental window

  
• Boundary setting

  
• Gene-environment correlation


  Passive gene-environment correlation

  • Predisposition correlates with environment, (family with genetic predisposition for football talent is more likely to play football with their child)

  Evocative gene-environment correlation

  • Inherited tendencies evoke certain responses from others (child with a genetic predisposition to behavioural problems may evoke harsher parenting)

  Active gene-environment correlation

  • Genetic make-up encourages “niche picking”, (child with a genetic predisposition for football talent actively chooses to join football club)
• Twin research


  Estimate of relative importance of genetic factors (‘heritability’)

  • h 2 = 2x(rMZ – rDZ)
  • Example: Heritability verbal fluency in 18y/o twins
  • h 2 = 2x (.51-.32) = 2x(.19) = .38
  • → Verbal fluency is moderately heritable in late adolescence

  
• Twin research: Focus on individual differences

  Genetic influence on variance, not on mean

  
• Twin research: advantage and disadvantage

  • Advantage: allows us to estimate the relative contributions of genes vs environment in explaining individual variation in a trait
  • Disadvantage: standard ‘classic’ twin design can not tell us about importance of gene-environment interaction or gene-environment correlation
• Causes within vs between groups

  Causes of average differences between groups are not necessarily related to the causes of individual differences within groups

  Example:

  • Height is strongly heritable within population
  • Differences in height between populations might be due to genetic differences, but also to e.g. differences in nutrition
• Genetics of behaviour and cognition

  Examines genetic variants associated with traits or disorders

  
• Genetics of behaviour and cognition

  
• Autism


  Twin studies show that autism is highly heritable

  Molecular genetic studies indicate that there is not one gene for autism: ⎼

  • Different genes may be involved in different people with autism
  • Within each individual, a combination of different genes may have contributed to the development of autism

  → Autism is genetically heterogeneous and polygenic