Behavioural genetics Flashcards
What is evolution?
- Individuals are similar but not identical
- Characteristics passed from parent to offspring
- Not all individuals survive to pass on their genes
- Characteristics that confer survival and mating advantage will survive into future generations and become more common
Genes
- Set of instructions for running the body
- Reside on strands of DNA
- RNA enters nucleus of the cell to
pick up the instructions from the gene
(transcription) - Returns to the rest of the cell where it gathers a
specific group of amino acids that form
a particular protein (translation) - Proteins are the building blocks of life
Genotypes
- Transmitted across generations
- Explains why people canbe a carrier for a gene
- Changes to the phenotype during individual’s lifetime are not passed on to offspring
Phenotype
- Biological/physical/behavioural/psychological trait caused by an individual’s genotype
- Majority of cells in body contribute to maintaining phenotype (e.g.,liver cells)
Gamets
- Few cells concerned with making more genotypes (eggs in females and sperm in males)
Chromosomes
- Tightly wound lengths of DNA
How does variation emerge?: Recombination
- DNA exchanged between paired chromosomes in stage before meiosis (gamate formation)
- Happens every time gamete is formed
- Increases variation even further
How does variation emerge?: Linkage
- Genes that reside in close proximity on the strand of DNA tend to be inherited together (travel together)
How does variation emerge?: Mutation
- Segmental duplications
- Chunks of DNA make an extra copy of itself during replication so now extra genes that are also subject to mutations that lead to some new function
- Gene families – multiple genes descended from a common ancestor by duplication events
- If this leads to some phenotype that confers survival or mating advantage, then natural selection will retain that trait within the population
- Vast majority of mutations either don’t lead to any type of phenotypic effect, or are detrimental to the individual
Alleles
- Different versions of the same gene
- Dominant or recessive
- Single gene charcteristics- where allele causes one phenotype (eg; traits like red hair)
Genes and behaviour
- Link between genes and behaviour is changes in neuronal or hormonal mechanisms
- Behaviour as a phenotype
- Monoamine oxidase- enzyme from the MAOA gene located on the chromosome – helps regulate serotonin
Genes and behaviour: Burner et al (1993)
- Study of dutch extended family
- Number of male relatives had severe conduct disorder (violence, rape and arson)
- Men found to have absence of MAOA activity
- MAOA was sequenced and found gene no longer coded correctly for amino acids
Quantitative genetics
- Estimates extent observed differences among individuals are due to genetic differences and environmental differences without specifying what those factors are
- Produces “heritability estimate”
Heritability
- Proportion of pheotypic variance that can account for by genetic differences in individuals
- Does not refer to genetic contribution to a trait
- Estimated from correlations between blood relatives
How to estimate heritability: Adoptive designs
- Genetic and environmental causation of behaviour estimated by looking at behavioural similarities and differences between genetically related individuals growing up in different environments
- Early research showed on average, genetics contribute (around 50%) to personality traits
- Schizophrenia (Heston, 1966)- found children of Schizophrenic parents just as likely to develop schizophrenia irrespective of whether they grow up with their birth or adoptive parents
How to estimate heritability: Twin designs
- Comparison of monozygotic (genetically identical) and dizygotic twins (same relatedness as siblings)
- Monozygotic twins should be phenotypically more similar than dizygotic twins
Interpreting heritability
- Both genetic and environmental influences contribute to educational attainment
- When child experience differences in quality of education and upbringing, then heritability is reduced because of the greater contribution from environmental influences
- Heritability describes what is in a population at a particular time
Shared environmental influences
- Non-genetic influences that make family members similar to each other
- Appear to contribute little to personality traits and cognitive abilities
- Family resemblance that is not explained by genetics
- Resemblance amongst adoptive relatives
Non-shared environmental influence
- Non-genetic influences that are independent for family members
- Your individual experience growing up that is unique to you
- Anything that is left after removing the genetic and shared-environmental influence
- Twin studies – birth weight, parental negativity -> behaviour problems and academic achievement, but also mediated by genes
How genetics shape environment
- Shared positive affect & responsiveness in 3-year-olds and their parents (Deater-Deckard & O’Connor, 2000)
- Family relations such as marital quality and parenting (Ganiban et al., 2009)
- Relationships & control of finances
- Friends and peer groups
- Perception of classroom environment (Walker & Plomin, 2006)
- Television (Plomin et al., 1990)
- Work environments (Hershberger et al., 1994)
- Social support (multiple studies)
- Exposure to drugs (Tsuang et al. 1992)
Types of genotype x environment correlation (Plomin et al., 1977)- Passive
Children receive genotypes correlated with their family environment
Types of genotype x environment correlation (Plomin et al., 1977)- Evocative
Individuals are reacted to on the basis of their genetic propensities
Types of genotype x environment correlation (Plomin et al., 1977)- Active
Individuals seek or create environments correlated with their genetic proclivities
Gene x environment interaction
- Genetic sensitivity or susceptibility to environments
- Effect of environment on a phenotype depends on genotype
- Effect of the genotype on the phenotype depends on the environment
Bohman, 1996; Brennan et al., 1996
- Adoptees whose birth parents have criminal convictions, are at risk of criminal behaviour (genetic)
- Adoptees whose adoptive parents have criminal convictions are at risk of criminal behaviour (environmental)
- Criminal convictions of adoptive parents led to increased criminal convictions of their adopted children more so when adoptee’s birth parents also had criminal convictions
Leve et al., 2010
- Adopted children whose birth parents had more psychopathology symptoms benefit from adopted mother’s structured interactions at 18 months old
- Children whose adopted parents who had psychopathology symptoms were at risk for developing behavioural problems- only when birth parents were high in psychopathology
Kendler et al., 1995
Effect of stressful life events on depression are worse for individuals at genetic risk for depression
Jaffee et al., 2005
Effect of physical maltreatment on conduct problems is greater for children at genetic risk for conduct problems
Hanscombe et al., 2012
Socioeconomic status does not moderate the heritability of children’s intelligence
Tuvblad et al., 2006
High heritability of adolescent antisocial behaviour in economically advantaged families
Feinberg et al., 2007
High heritability for adolescent antisocial behaviour when parenting is negative
MAOA gene (Caspi et al., 2002):
- No difference in behavioural outcome for children with low or high MAOA genotype in the absence of child maltreatment
- Children with MAOA genotype developed antisocial behaviour when exposed to child maltreatment
5-HTTLPR serotonin transporter gene (Caspi et al., 2003):
- No difference in relationship between gene and depressive symptoms in absence of stressful life events
- Presence of depression significantly higher in presence of gene and an increasing number of stressful life events
Schizophrenia
- Delusions, hallucinations, disorganised speech and behaviour, low emotionality, & lack of motivation
- General population – risk of 1%
- Second degree relatives – 4%
- First degree relatives– 9% (For offspring – 13%)
- Identical twin – 46%
Schizophrenia & adoption studies: Heston, 1966
Risk of schizophrenia in adopted children whose birth mother is schizophrenic is 11% compared to adoptees whose birth parents do not have schizophrenia (0-1%)
Schizophrenia & adoption studies: Tienari et al., 2004
10% of adoptees with schizophrenic parents report some form of psychosis (rate of 1% in adoptees without schizophrenic parents)
Schizophrenia & adoption studies: Kety et al., 1994)
Schizophrenia is not influenced by the home environment fostered by schizophrenic parents
Major depressive disorder (MDD) & bipolar disorder (BD): Family studies
- Increased risk for first degree relatives – 9%
- MTHFR gene variant implicated
- Early onset, drug use & suicide attempts, response to medication potentially more heritable in BD (Smoller & Finn, 2003; Schulze et al. 2006; grof et al., 2002)
Major depressive disorder (MDD) & bipolar disorder (BD): Twin studies
- MDD – 38% (no shared environmental influence; Kendler et al., 2006), but maybe as much as 70% (McGuffin et al., 1996)
- Concordance rates for MZ /DZ twins – 43%/28%
- BD – Concordance rates for MZ /DZ twins – 65/7%; 40/5%; 55/7%
Autism/ASDs
- Twin studies show high concordance rates for MZ twins far beyond DZ twins (at least 60%)
- Now considered one of the most heritable conditions (Freitag, 2007; Ronald & Hoekstra, 2011)
- Genetic influence is the same irrespective of severity
- 3 impairments of autism: poor social interaction, language & communication problems, and restricted range of interests and activities are influenced by different genes
- 100 genes are associated
- Some cases due to rare mutations (only 10%)
ADHD
- First degree relatives 5 times more likely to be diagnosed (Biederman et al., 1992)
- Research consistently demonstrated strong genetic influence for the hyperactivity component, perhaps up to 76% heritability
- Heritability greater for ADHD which continues into adulthood
- Substantial genetic overlap for the inattention and hyperactivity components of ADHD
Co-occurrence of disorders
- High levels of comorbidity
- Genetic overlaps between MDD and BD, and BD and schizophrenia
- Genetic overlap among anxiety disorders – differences caused by non-shared environmental factors
- Anxiety and depression caused by the same genetic factors (Kendler et al., 1992)
- Non-shared environmental influences appear to be the differentiating factor (Kendler 1996; Mddeldorp et al., 2005)
Genetics research suggests two over-arching categories of disorders: Internalising
Anxious/misery
- Major depression/GAD/Panic disorder
Fear:
- Panic disorder/animal phobia/situational phobia
Genetics research suggests two over-arching categories of disorders: Externalising
Alcohol dependence/other drug abuse or dependence/antisocial behaviour/CD
Personality: Loehlin & Nichols (1976)
- Nearly all personality traits show moderate heritability (30 – 50%)
- Environmental influence not to do with parents but actually non-shared environment
Other FFM traits
- Openness to experience – 45%
- Conscientiousness – 38%
- Agreeableness – 35%
(Loehlin, 1992; Jang et al., 1996) - Sensation seeking (60%) (Fulker et al., 1980; Koopmans et al., 1995)
Other contexts: Situational change
- In a lab task, identical twins changed similarly in adapting to different tasks than non-identical twins (Mateny & Dolan, 1975)
- Genetic influence in stability of shyness in different situations (Cherny et al., 1994)
- Personality trait changes across different situations (Dworkin, 1979)
- Genetic influence in how people respond to personality questionnaires (Eaves & Eysenck, 1976; Hershberger et al., 1995)
Other Contexts: Relationships
Parent-offspring:
- Attachment – moderate heritability, but substantial shared environmental influence
Romantic
- Quality of relationship (15 – 35%)
- About 50% of relationship quality affected by personality – so indirectly by genetics
Other Contexts: Sexual Orientation
- 34-39% for men (+ non-shared environments)
- 20% for women (+ modest shared environmental influence) (Langstrom et al., 2010
Other Contexts: Self esteem
Modest genetic influence, but no influence for shared family environment
Other Contexts: Attitudes and interests
Traditionalism, sexual & religious attitudes – 50% genetic, shared environment – 15%
(Eaves et al., 1989; Olson et al., 2001)
Personality disorders
- Different from psychopathology as people affected consider it as part of their personality, rather than a condition
Schizotypal PD
- Less intense version of schizophrenia
- Runs in families
- 33% concordance rate for MZ twins, and 4% for DZ twins (Torgersen et al., 2000)
- Risks of schizotypal personality disorder are 11% for first-degree relatives
- Twin study suggests negative and positive aspects of schizotypy differ genetically (Linney et al., 2003)
- Schizotypy is genetically related to schizophrenia (Jang et al., 2005)
ASPD
- Risk for ASPD increased 5x for first degree relatives of ASPD males
Antisocial behaviour:
- Genetics – 40%; shared environmental influence – 15%; non-shared – 16% (Rhee & Waldman, 2002)
- Non-shared environment contributes to change as individual gets older (Burt et al., 2010)
- Increased rate of ASPD in the adopted children of birth parents with criminal records (Cadoret & Stewart, 1991; Crowe, 1974)
Criminal behaviour
- Concordance rate: 52% MZ twins; 21% DZ twins
- Adopted children greater risk for criminal behaviour when birth parents have criminal convictions (Mednick et al., 1984)
- Appears to be for property crimes not violent
- G x E interaction – adopted children greater risk if both adopted and birth parents engage in criminal activity (Beaver, 2011)
- Twin studies might over-emphasise genetic effects – partners in crime
- Genetic influence contributes to both ASPD and substance use disorders:
- Adoptees (male & female) increased biological risk for ASPD – increased aggressiveness, CP, ASPD and substance dependence (Cadoret et al., 1995; Cadoret et al., 1996)
