Lecture 13 - Genetic effects on behaviour Flashcards
What shapes our behaviour as adults?
- What we inherit from parents: via genes & mDNA (mitochondria)
- What we experience through life: env. hormones/toxins/stress/drugs etc
- Both interact e.g genes predispose us to a particular environment or the env can change gene expression
- Individual differences: things are also randomised developmental processes e.g genetically identical fish in identical env had diff personalities
How do we know that genes influence behaviour?
- Animal studies: selective breeding e.g friendly foxes had tame offspring = genetic factor mediated temperament
- Animal studies: incest of mice = all mice would be genetically identical eventually & can deliberately mutate genes
- Human studies: Family, twin, adoption, effects of mutation
Describe family studies:
- Degree of relatedness decreases = lower gene transference
Unrelated individuals share small proportion of original individual’s genetic variants - Similar pattern observed for shared env e.g diff env for grandparents adn kids etc.
Describe twin studies:
- MZ twins share 100% of DNA, DZ share only 50%
- Twins usually raised in identical env
- Are twins representative of the population e.g sharing placenta/born smaller
- Looking at concordance rates to see if genetic influence over behaviour inc. schiz
Describe adoption studies
- Adopted kids share genes but not env with bio but share env with adopted
- If trait is genetically influenced, greater connection between trait in adopted kid and bio fam
What are the issues with adoption studies?
- Info on adoptee/bio families may not be available
- Ethics on approaching bio family after adoption
- Adoption process not random & not representative of general population e.g stable fam & bio parents struggle
- Adopted children subjected to bio mum’s utero env
- Adoption is rare in developed western countries = small sample size
What were classical adoption studies?
1) Compared 47 adopted children whos bio mums had/not schiz. 17% of g1 developed schiz but 0% of g2 did
2) Identified large no. of adults with/out schiz who were adopted
- 13% of bio relatives of adoptees with schiz had schiz-like disorders
What is an alternative type of study for dissociating between genetic and env influences
- Homologous IVF = both parents related to baby
- IVF with sperm donation = mum only
- IVF with egg donation = dad only
- IVF with embryo donation = neither
What was the IVF study?
- Looked at measures of maternal smoking, child birthweight and psychological profile
- If mum smoked = born smaller = regardless of bio/IVF
- Maternal smoking = antisocial behaviour ONLY when kid was genetically related
How do we quantify genetic effects?
Equation: 2 x difference in correlations between MZ and DZ twins
- High heritability does not mean trait is unaffected by env
- Trait may have perfect heritability but can change from env
What causes heritability to change?
- As env becomes less variable, heritability increases
- As env is more variable = heritability decreases
What is missing heritability? Why does it happen?
- Gap between heritability estimates and known effects of genes
- Failure to identify all causal genetic variants
- Neglect of sex chromosomes
- Complex interactions between genetic variants and env
- Overestimation of heritability e.g twin studies
What are the two types of genes that cause disease
- Complex: many variants of small effect
- Polygenic: few variants of larger effect
- Both interact with environment
- Genes are not deterministic
What are the challenges with identifying associated genetic factors?
- Large sample size needed
- Difficulty ensuring consistent diagnosis
- Population stratification
- Hard assigning causality
- Controversy e.g looking at if genes cause homosexuality
What are rare variants that could influence genes (SAAME)
MAO COMT gene could have Brunner syndrome
- Aggression
- Arson
- Sexual violence
- exhibitionism
- Mood/Sleep problems
