PSYC 2600 Lecture Notes - Lecture 4: Human Genome Project, Selective Breeding, Heritability

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Genetics and Personality January 30, 2018
Biology measuring the systems of the body that influence our behaviour and our
personality
The Human Genome
Human genome (dictionary) refers to the complete set of genes than an
organism possesses
Human genome contains tens of thousands of genes on 23 pairs of
chromosomes
Human genome project is designed to sequence the entire human genome
example: identify the particular sequence of DNA molecules in the human
species
But identifying sequence of DNA molecules does not mean identifying the
function of each molecule
Sequencing the human genome
Most genes in a human genome are the same for all humans
Small number of genes are different for different individuals, including genes
that indirectly code for physical traits and for personality traits
One genome per person. Most genes are the same for all of us. That one book
shares about 99% of its material with monkeys, the 1% that makes us different
from monkeys and each other
Controversy About Genes and Personality
Behavioural geneticists attempt to determine the degree to which individual
differences in personality are caused by genetic and environmental
differences
Highly controversial
o Ideological concerns about findings being misused
o Concerns about renewed interest in eugenics
Modern behavioural geneticists who study personality are typically very
careful about addressing implications of work and are sensitive to ideological
concerns
o Knowledge is better than ignorance
Pro you can screen for unwanted genes (diseases), identify psychological
traits (predispositions to delinquency) and give them help to prevent
Con we can’t control the environment, we don’t know what we’re messing
with, human variability may be crucial for survival
Important Take Home
Finding that a personality trait has a genetic component does not mean the
environment is powerless to modify trait
2 Goals of Behavioural Genetics
1. Determine % of individual differences in a trait that can be attributed to:
genetic differences and environmental differences
2. Determine the ways in which genes and environment interact and correlate
with each other to produce individual differences
Goal 1 Identify Heritability vs. Environmentality
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Heritability proportion of observed variance in group of individuals that
can be explained or accounted for by genetic variance
o Proportion of phenotypic variance that is attributable to genotypic
variance
o When we talk about heritability, we are always talking about a group
Environmentality proportion of observed variance in group of individuals
attributable to (non-genetic) environmental variance
Example if heritability of a personality trait is .70, then genes account for
70% of observed (phenotypic) variation and environmental accounts for
30%
Misconceptions About Heritability
Heritability CANNOT be applied to single individual
o Only relevant for discussion of group-level variation
Heritability is NOT constant or immutable
o Can change over time and can be different in different populations
Heritability is not a precise statistic
o Based on correlations, which by nature have degree of imprecision
and fluctuation across samples
Behavioural Genetics Methods
1. Selective breeding
- Cannot be ethically conducted with humans
- Selective breeding studies of…
- Can only occur if a desired trait is heritable
2. Family studies
- Correlates the degree of genetic overlap among family
members with the degree of similarity in personality trait
- If a trait is highly heritable, family members with greater
genetic relatedness should be more similar to one another on
the trait than family members who are less closely genetically
related
- Problem: members of a family who share the same genes also
usually share the same environment confounds genetic with
environmental influences. Thus, family studies are never
definitive
3. Twin studies
- Estimates heritability by gauging whether identical (MZ) twins,
who share 100% of genes, are more similar then fraternal (DZ)
twins, who share only 50% of genes
- If MZ twins are more similar than DZ twins, this provides
evidence of heritability
- Two assumptions
Equal environments assumption environments
experienced by MZ twins are no more similar than
those experienced by fraternal twins (assumption has
largely been supported; sometimes violated)
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