L3 & 4 - Behavioural Genetics

Question 1

Where does the heritability index come from?

Answer 1

• Use a ‘naturalistic experiment’ to estimate the extent of heritability
  
  • Due to existence of twins
    
    • Monozygotic - Identical (shared common environment and 100% genes)
    • Dizygotic - Non-Identical (shared common environment and 50% genes)

Question 2

What are the two statistical construct crucial to understanding twin studies?

Answer 2

• Correlation
  
  • Is there a systematic relationship between Twin 1 & 2?
  • Correlation is stronger for MZ than DZ
  • Also a linear pattern
• Variation
  
  • How points are distributed over the measurement scale/spread out around the line
  • You can see the range is the same for MZ and DZ
  • Less variance for MZ
  • Stats = Variance should be equal for different groups

Stats = Variance should be equal for different groups

Question 3

What is the heritability index calculation?

Answer 3

• Phenotype (P) = Genetic effects (G) + Environmental effects (E) or 1 = h2 + environmental effects (E)
  
  • If we work out environmental effects, we know heritability but environment is two parts
• Types of environment
  
  • Common environment → Events that happen to both twins, influencing them in the same way
    
    • e.g. same family members, same house
  • Unique environment → Events that occur to one twin but not the other, or events that happen to both twins but influence them in
  • Phenotype (P) = Genetic effects (G) + Common environment (C) + Unique environment (E)
    
    • 1 = h2 + C + E
  • Final equations
    
    • Rmz = h2 + C
    • Rdz = ½ h2 + C
    • H2 = 2(rmz – rdz)
      
      • h2 = twice the difference between identical and fraternal twin correlations

Question 4

What are the issues with the heritability index?

Answer 4

• In some examples, heritability could be higher than 1 which is not possible
• Makes assumptions of additive genetic effects/narrow sense heritability
  
  • The idea that risk conferred by allele is r-fold for heterozygotes and 2r-fold for homozygotes
    
    • Aa = rAA
    • Aa = 2rAA
  • BUT THIS ASSUMPTION IS WRONG
    
    • Effects can be dominant, recessive, heterozygous
    • Gene-gene interactions
    • Gene-environment interactions
• Additive genetic effects are still part of a nice simple model and will be called A in models
• Phenotype (P) = additive genetic effects (A) + common environment (C) + Unique environment (E)

Question 5

What is the evidence for criticisms of the twin model?

Answer 5

• Burt (2009)
  
  • Meta-analysis of 490 studies of internalizing and externalizing psychopathology prior to adulthood
  • Traditional studies – Say additive genetic effect and non-shared environment are of great importance for psychopathology – no influence of shared environment
    
    • HOWEVER – shared environment was found by literature to be important prior to adulthood and especially in more extreme environments
  • Concluded
    
    • Shared environment accounted for modest to moderate amount of variance in psychopathology outcomes for every domain except ADHP
    • It is also notable that the non-shared environment (e2) also had an impact on psychopathology, even in the case of ADHP

Question 6

How does the shared environment influence child psychopathology?

Answer 6

• Increasing evidence shows that certain parenting styles & behaviours can increase the children’s risks for psychopathology outcomes
• Parental over-protection and over-control promotes children’s anxiety
• Parental hostility and poor boundary setting increase the likelihood that children will have externalizing problems
• Externalizing problems in childhood are the best predictor of all the common forms of mental health problems in adulthood
• It matters when you measure something and how you measure it (balance between unique and shared environment)

Question 7

What is the missing heritability problem?

Answer 7

• Finding the source of why traits can be heritable is unknown
• Replications of gene-disorder are rare = Even when found only a small proportion of the diagnostic phenotype are attributable to common genetic variations
• Only a few genotypes have been found to be reliably associated

Question 8

What are the different reasons why we have the missing heritability problem?

Answer 8

1. We are not looking at the correct genes
   
   • Hypothesis-driven research has had the wrong hypothesis
   • Functionality of genes
     
     • Genes don’t do what we think they do or it is not a singular gene but a gene network/gene-gene interactions
     • Proteins don’t do what we think they do
   • Relationship between protein function and biological function
     
     • Proteins don’t do what we think they do
     • Proteins don’t influence brain function as we think (sometimes different neurotransmitters have different uses depending on where they are in the body)
2. We are not looking at the right samples
   
   • Samples need to be as “pure” as possible
     
     • Overlap between phenotypes with different aetiologies (causes)
     • Different distribution of genotypes in different ethnicities
     • Range of descriptive too large
   • Sometimes the phenotype may not be clear until a certain age (abnormal vs normal development)
3. We are not thinking about it in the right way (e.g. gene-gene interactions) & Epigenetics (explored further down)
   
   • Interaction → Where one variable influences the relationship between two other variables

Question 9

What are interactions, mediation and moderation?

Answer 9

• Interactions – One variable influences the relationships between two other variables
• Mediation → Mediator variables specify how or why a particular effect/relationship occur
  
  • e.g. time spent doing homework is associated with better exam performance but this is mediated by doing practice papers
  • Commonly refers to understanding the association between the genotype and phenotype
    
    • e.g. Serotonin 1B associated with callous-unemotional traits but what mediates the relationship between them
• Moderation → Changes the strength of an effect or relationship between the two variables/When a genotype changes the relationship between an environmental independent variable and a dependent variable
  
  • Moderators indicate when or under what conditions a particular effect can be expected
  • Moderator may increase the strength of a relationship, decrease the strength of a relationship, or change the direction of a relationship
    
    • e.g. after 120 minutes of revising there is negative retention
  • If moderation is not accounted for = Only showing the average of the two

Question 10

What is susceptibility?

Answer 10

• Need to consider parenting behaviours alongside genetics
• Differential susceptibility to the environment – Each person will be impacted differently by the environment
  
  • Highly susceptible = Negative development in a negative environment but positive development in a positive environment
  • Low susceptibility = No developmental vulnerability in negative conditions and no developmental enhancement in positive conditions (remains the same)
  • Orchid child vs Dandelion child (will thrive anywhere)
    -
• Research study (Albert et al. 2015) – Can genetics predict complex Behavioural intervention?
  
  • High risk children with genes for a poor social-stress response were compared
  • Found orchid children with this variant reduced in behavior with psychosocial intervention but dandelion children remained the same (less sensitive to the environment)

Question 11

What are epigenetics?

Answer 11

• Epigenetics → Functionally relevant changes to the genome that do not include a change in the nucleotide sequence
• Dynamic alterations in the transcriptional potential of a cell (e.g. such as methylation → the changes in how your DNA is read)
• Environmental stressors can impact methylation and have later life consequences with disorders

Question 12

How does epigenetics help answer the missing heritability problem?

Answer 12

• Offers a plausible solution to the missing heritability problem
  
  • Genotype alone does not dictate gene expression
  • A mechanism for gene-environment interactions
• Provides a challenge
  
  • Further interactions – genotypic effects on methylation
• Provides hope as epigenetics is a dynamic process
  
  • Can be slowed down, sped up, prevented, reversed
• Sheds light potentially on critical periods etc.
• Is exciting – paradigm shift as new field?
• Important to psychology as we can’t ignore the lower levels