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Lecture 5

PSYB30H3 Lecture Notes - Lecture 5: Positron Emission Tomography, Evoked Potential, Working Memory

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Lisa Fiksenbaum

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PSYB30 Lecture 5
Twins raised apart and other unusual parents:
Major Findings from Behavioural Genetic Research
Summaries of behavioural genetic data yield heritability estimates for major personality traits (5
big traits) of about 20-45 percent
Sexual orientation
o Controversial and developing area
o Current evidence suggest that genes provide modest and indirect influence (via
childhood gender nonconformity) on adult sexual orientations
Attitudes and preferences
o Wide variance in heritability of attitudes
o Some attitudes show high heritability whereas others show low or no heritability
Drinking and Smoking
o Behavioural manifestations of personality traits such sensation seeking, extraversion,
o Drinking alcohol and smoking cigarettes are stable over time
o Both show evidence of heritability
Heritability of Happiness
Lykken & Tellegen measured happiness, or subjective well-being, on a birth-record-based
sample of 2,310 middle-aged twins
Measured happiness using the Well-Being (WB) scale of the Multidimensional Personality
Questionnaire, SES, educational attainment, family income, marital status, and religious
o None of these variables could account for more than about 3% of the variance in well-
o From 44-52% of the variance in well-being, however, is associated with genetic variation
o Re-test smaller samples of twins after intervals of 4.5 years and 10 years
o Authors estimate that heritability of stable component of subjective well-being
approaches 80%
Genetic Influence on Risk of Divorce
McGue and Lykken (1992) explored the separate influence of genetic and environmental factors
on risk of divorce by examining divorce status of 1,516 same-sex twin pairs (722 monozygotic
[MZ] ad 79 dizgoti [DZ]), thei paets, ad thei spouses’ paets
Concordance for divorce was significantly higher in MZ than DZ twins
The robustness and magnitude of the MZ-D difference in divorce concordance indicates a strong
influence of genetic factors in the etiology of divorce
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Moeoe, fail akgoud of oth spouses otiuted idepedetl to ouples’ dioe
Does a Sense of Humour Run in Families?
Using a sample of MZ and DZ female pairs, Johnson et al. (2008) had each twin rate how funny
they found a series of five Far Side cartoons
Researchers were careful to have the women rate the cartoons in separate rooms so they
ould’t see o hea thei ti’s eatios
Results: the ratings of each twin were pretty similar for each of the 5 cartoons
o The correlation between ratings of one MZ with her twin was 0.50 and for DZ twins it
was 0.41
Are these correlations different enough to suggest a genetic component?
Researchers tested this idea using advanced stat procedures and found that there was no
significant impact of genetics on the ratings of these cartoons
They estimated that about 49% of the differences between twin pairs was due to differences in
shared environment whereas 51% was due to non-shared environment
Conclusion: sense of humour is something that is pretty learned at home, and partly picked up
fo fieds, ad othe aspets of a idiidual’s uiue eioet
Shared Versus Non-Shared Environmental Influences: A Riddle
Same studies that suggest moderate heritability also provide good evidence of the importance
of environmental influences
Personality characteristics show heritability in 3050 percent range; hence, showing substantial
degree of environmentality5070 percent
For most personality traits, the environment has major influence, but this influence is primarily
in the form of non-shared and not shared variables
For most personality traits, the shared environment has little impact
We do not know which non-shared experiences have a key impact on personality
Genotype-Environment Correlation
Differential exposure of individuals with different genotypes to different environments
Genotype-environment correlations can be positive or negative
Three types of genotype-environment correlations
o Passive
o Reactive
o Active
Molecular Geneticsz
Techniques designed to identify specific genes associated with personality traits
D4DRgene located on the short arm of chromosome 11, codes for dopamine receptor
o Most frequently examined association between D4DR gene and a personality trait
ioles oelt seekig
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