lecture 15 - genetic effects on behaviour Flashcards
(25 cards)
what we inherit + what we experience = how we behave
we inherit - sperm and egg molecules, mitochondria ‘mDNA’, Genomic DNA ‘genes’
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what we experience - throughout life ‘environment’
eg toxins, hormone, diet, stress, infection, injury, drugs, social interaction
individual differences
an additional role for stochastic (‘random’) developmental processes
also influences our behaviour as affects body physiology
how do we know that genes influence behaviour?
in animals
- selective breeding eg ‘Russian silver fox experiment’ how wild dogs domesticated, tame males bred with tame females then next generation and again and again so tame gene = dominant - side effect morphology changed - cuter eg floppy ears -pliotropy
- black six mice - used in studies - 1930s bred fancy mice - can inbreed mice - overtime become genticllay identical = inbred strays
effects of mutations - mess around with DNA and genes look at mammals and non-mammals
humans
- family studies
- twin studies
- adoption studies
- effects of ‘variants’
family studies
‘As relatedness decreases, so does the common genetic complement’
more related more genetic material share
* An unrelated individual shares a small proportion of the original individual’s genetic variants
* However, similar pattern observed for shared environment
twin studies
- Identical (monozygotic) twins share 100% of one another’s genetic material; non-identical (dizygotic, fraternal) twins share, on average, 50% of one another’s genetic material (= siblings)
- Twins generally raised in identical environments
- Are twins representative of general population?
‘If a behavioural trait is genetically influenced, expect greater similarity between individuals with greater relatedness’
higher Sz risk in twins
similar in IQ and personality traits - higher correlation
twin studies - look at similarity on a characteristic and correlation coefficient is how similar they are to one another
genain quadraplets - all have sz - genetic factors in family
adoption studies
- Adopted children share their genetic material, but not their environment, with their biological parents/siblings
- They share their environment, but not their genetic material, with their adoptive parents/siblings
‘If a trait is genetically influenced, there should be a greater correlation between the trait in adopted children
and their biological parents and siblings, than between the trait in children and their adoptive family
Powerful studies, but difficult to undertake:
- Information on adoptee and biological families may not be available
- Ethical issues re approaching biological family about child adopted away
- Adoption process not random e.g. adopted children placed in non-representative families
- Adopted children not representative of general population
- Adopted children subjected to biological mother’s in utero
environment and early life influences - Adoption rare in developed Western countries
i.e. small sample size
Some ‘adoption study’ evidence for genetic influences on psychological traits and psychiatric illness:
Heston (1966):
- Compared 47 adopted children whose biological mothers had schizophrenia (Group 1), to adopted children whose mothers did not have schizophrenia (Group 2)
- 17% of Group 1 developed schizophrenia vs. 0% of Group 2
Danish adoption study (1980-): - Identified large number of adults with and without SCZ who had been adopted shortly after birth
- 13% of biological relatives of adoptees with SCZ had SCZ-like disorders vs. 1% of biological relatives of adoptees without SCZ
An alternative type of study for dissociating between genetic and environmental influences…
- Exploits ‘experiment of nature’: increased use of in vitro fertilisation (IVF) techniques
Type of IVF procedure then Parent related to child
Homologous IVF Both
IVF with sperm donation Mother only
IVF with egg donation Father only
IVF with embryo donation Neither
Rice et al. (2009) PNAS 106(7): 2464-2467
different genetic relationships - look at that and environment and how impacts behaviour
779 IVF-related pregnancies and resultant children closely monitored:
- Maternal smoking
- Child’s birthweight
- Child’s psychological profile (e.g. antisocial behaviour)
- Positive association between variables in pregnancies where mother is genetically unrelated to offspring (IVF with egg or embryo donation) cannot be due to inherited factors from the mother (genetics)
Positive association between variables in pregnancies where mother is genetically related to offspring (homologous IVF, or IVF with sperm donation) suggests influence of heritable factors
Results
- Prenatal exposure to smoking in related/unrelated offspring resulted in lower birthweights
Significant association between maternal smoking and antisocial behaviour in related, but not unrelated group: role for underlying inherited factors
Quantification of genetic effects
- Family, twin and adoption studies allow ‘heritability’ calculation
‘the proportion of variance in a trait which is attributable to genetic variation within a defined population in a specific environment’
~2x difference in correlation between MZ and DZ twins i.e. Falconer’s formula:
H2=2(r(MZ)-r(DZ)) - difference in correlation strength between mz twins and dz twins - High heritability does not mean that the trait is unaffected by the environment
A trait may have perfect heritability in a population, and still be subject to great changes resulting from environmental variation
Children -Biological parents - Adoptive parents
110 -90 -118
112 -92 -114
114- 94 -110
116 -96 -120
118 -98 -112
120 -100 -116
Mean: 115 -Mean: 95 - Mean:115
images in notes
shape of eye influenced strongly by genetics
environment and heritability
- As the environment becomes less variable, trait heritability increases
- As the environment becomes more variable, trait heritability decreases
heritability of diseases
generalised anxiety disorder = 20%
panic disorder = 30%
major depression males = 30%
major depression females = 40%
alcohol dependence = 55%
alzheimers disease = 65%
bipolar disorder = 80%
sz = 80%
autism = 90%
However, gap between heritability estimates and combined, known effects of individual
genes: ‘missing heritability’ (Nature Reviews Genetics 11: 446-450
Why?
* Failure to identify all causal genetic variants
* Neglect of sex chromosomes
* Complex interactions between genetic variants (‘epistasis’), and between genetic variants
and the environment
* Over-estimation of heritability from e.g. twin studies
‘any dispassionate reading of the evidence leads to the inescapable conclusion that genetic factors play a substantial role I’m the origins of individual differences with report to all psychological traits, both normal and abnormal’
genes and traits
- How traits are inherited within families can give clues as to the number and type of genetic
variants involved - Behavioural traits and psychiatric illness risk are typically underpinned by ‘many variants of
small effect’ and ‘few variants of larger effect’ (complex, polygenic), and by interactions with
the environment - Sets of genetic variants may predispose to particular behaviour patterns, but are not
deterministic
‘a gene for criminality…’
‘a gene for homosexuality….’
‘a gene for intelligence…
Challenges with identifying associated genetic factors
- Large numbers of subjects required to detect small effect sizes
- Difficulty ensuring consistent diagnosis/phenotyping of pooled samples
- Population stratification
- Difficulty assigning causality - differences around the world between gender and culture
Controversy e.g. homosexuality
Genetic conditions with behavioural features
22q11.2 deletion syndrome
Turner syndrome
Down syndrome
Many more including Fragile X syndrome, Huntington’s Disease, X-linked ichthyosis etc
Effects of rare variants (‘mutations’)
Rare changes in some genes may substantially influence behaviour e.g. MAOA
Brunner syndrome:
* Impulsive aggression
* Arson
* Sexual violence
* Exhibitionism
* Mood and sleep problems
Brunner et al. (1993) Science 262:578-80
diagram in notes
Summary
- How we behave is influenced by: a) what we inherit (genes), b) our environment and c)
‘stochastic’ (chance) developmental processes in a complex manner - Family, twin, adoption and IVF studies can indicate the relative importance and specificity of
these factors, but are limited in important ways - Estimates for heritability can be drawn from these studies, but often these are inconsistent
with our current genetic knowledge - Healthy and pathological behaviour is influenced by the combination of many genetic variants
(most of small effect) whose expression can be modulated by the environment (‘nature vs.
nurture’) - Current studies are aiming to understand genetic mechanisms contributing towards important
psychological and psychiatric phenomena e.g. intelligence
Practice essay question:
‘How do we know that genes influence
behaviour?’
“Genetic and Environmental Influences on Human Psychological Differences” by Thomas J. Bouchard and Matt McGue:
- Introduction
- The article examines the relative influence of genetics and environment on human psychological traits.
- It discusses five major domains of individual differences: cognitive abilities, personality, social attitudes, psychological interests, and psychopathology.
- The authors review behavioral genetic methodologies, particularly twin and adoption studies, to assess heritability.
- Key Findings
A. Heritability of Psychological Traits- Virtually all reliably measured psychological traits show moderate to substantial heritability.
- Cognitive abilities (IQ) are highly heritable (~50%-80%), with genetic influence increasing with age.
- Personality traits are moderately heritable (~40%-60%) and show a hierarchical structure.
- Social attitudes and interests also show genetic influence, but environmental factors play a more significant role.
B. Role of Shared vs. Non-Shared Environment - Shared environment (family upbringing) has limited effects on most psychological traits beyond childhood.
- Non-shared environmental factors (unique individual experiences) are more influential in shaping differences between individuals.
- Twin and Adoption Studies
- Twin studies (comparing identical and fraternal twins) show strong genetic contributions to psychological traits.
- Adoption studies confirm that adopted children resemble their biological parents more than their adoptive parents in traits like IQ and personality.
- The heritability of intelligence increases with age, while shared environmental influence declines.
- Implications
- Findings challenge traditional views that family environment is the primary determinant of personality and intelligence.
- Genetics plays a significant role, but environmental influences still shape individual development.
- The research suggests a gene-environment interplay, where genetic predispositions influence how individuals react to their environments.
- Methodological Considerations
- The article highlights common misconceptions in interpreting genetic research, such as assuming genetic influence means traits are unchangeable.
- It also acknowledges criticisms of behavior genetic designs, including concerns about equal environments in twin studies and selection biases in adoption studies.
- Conclusion
- Genetics significantly influences psychological traits, but environment also plays a crucial role.
Future research should explore gene-environment interactions and the biological basis of cognitive and personality traits.
- Genetics significantly influences psychological traits, but environment also plays a crucial role.
