PSYC 2740 Lecture Notes - Lecture 6: Twin Study, Behavioural Genetics, Heritability

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16 Nov 2017
Lecture 6 - The Biological Domain: Genetics & Personality
Genes & Personality: Key Issues (Specific genes for determining traits?)
Why might the study of genes & personality be controversial?
o Eugenics (ability to engineer certain type of personality, include desirable
traits, not include undesirable, controversy)
o Ideology (if there is a biological information how does this effect
change/remediation ie. criminals)
Percent of variance
Difference between people due to a certain cause (in percentages)
Separated into different percentages, is it cause from genetics or environment
Heritability vs. environmentality
Heritability: Amount of phenotypic variance (what we can observe or measure) in
a group due to genotypic variance
o Genotypic Variance: Individual differences in people’s genes
Environmentality: Amount of observed variance due to environment
Behavioural genetics (BG) methodologies (how researchers determine, how strong
they are in determining data)
Family Studies
Twin Studies
Adoption Studies
BG Methods: Family studies (we would expect that people who are more closely related
are more similar with respect to these specific traits, correlation)
Examine correlations between:
o Genetic relatedness of family members (how similar they are - genetic)
o Personality similarity (should have more similarity if share more genes)
Family studies & shared genes (in %)
o Parents & children: 50%
o Siblings: 50%
o Grandparents & grandchildren: 25%
o Closer relatives should have more personality similarity (if trait due to
o Limited: not making account for similar environments they grow up in,
correlation not causation, may be other factors involved
BG Methods: Twin studies (restrictions to overall number of twins we can use in these
Monozygotic (MZ) Twins (share 100% of genes, clones)
Dizygotic (DZ) Twins (50%, as similar as regular siblings)
Estimate heritability via similarity of: MZ vs. DZ twins (compare them, should see
much more similarity between MZ vs. DZ)
Heritability = 2(rmz rdz) (ignore squared)
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