PSYC 2600 Lecture Notes - Selective Breeding, Jeffrey Alan Gray

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Personality Midterm Review
February 9, 2012
Chapter 6: Genetics & Personality
Definitions
Eugenics: The notion that we can design the future of the human species by fostering the
reproduction of persons with certain traits and by discouraging the reproduction of persons
without those traits
Percent of Variance: Individuals are different and this variability can be partitioned into
percentages that are due to different causes.
Heritability: Proportion of observed variance in group of individuals that can be explained or
accounted for by genetic variance (Ex. Long Black hair, do your parents have it also?)
Phenotype Variance: Observed individual differences (height, weight, personality)
Genotype Variance: Individual differences in the total collection of genes possessed by each
person
Environmentality: Proportion of observed variance in group of individuals attributable to
environmental influences
Goals and Methods of Behavioural Genetics
Determine the percentage of individual differences in a trait that can be attributed to genetic
differences and the percentage that can be attributed to environmental differences
Eg. Is the height of an individual due to genetics or environment (diet while growing)?
90% of individual differences has to do with genetics
Determine the ways in which genes and environment interact and correlate
with each other to produce individual differences. (We never say its 100% one
or the other)
Misconceptions About Heritability
The Belief that Heritability can be applied to an individual, however it can
NOT (must be applied as a generalization to samples and populations)
The Belief that Heritability is constant, but it is a statistic that applies only to
a population at one point in time and at a particular array of environments. (if
the environment changes than heritability can change to)
The Belief that heritability is an absolutely precise statistic however, it is far
from the truth as factors such as error and unreliability of measurements can
distort the statistics.
- Heritability is best regarded as merely an estimate of the percentage of
phenotypic differences due to genetic differences.
Research shows us that by finding that a personality trait has a genetic
component does not mean the environment is powerless to modify the trait
Behavioral Genetic Methods
Selective Breeding
Studies of Humans Best Friend
Selective breeding: The process of breeding plants and animals for particular genetic traits
Can only occur if a desired trait is heritable; gene can not be passed down if it is not heritable
Selective breeding studies of dogs- Identifying the desired trait in a dog and having them mate
with another with the same trait
Cannot be ethically conducted with humans
Family Studies
Correlate the degree of genetic relatedness among family members with the degree of personality
similarity and capitalize on the fact that there are known degrees of genetic overlap among family
members
Half of our genetic code comes from each parent – they each give us half of their genetic code
but we get a random selection
grandparents and grandchildren share about 25% of genes
Thus, our genetic code will be different (based on random selection) from the genetic code of our
siblings. On average, we share 50% of our genetic material with our siblings
Twin Studies
Estimate heritability by gauging if identical (monozygotic /MZ) twins (who share 100% of genes)
are more similar than fraternal (dizygotic/ DZ) twins (who share 50% of genes)
If MZ twins are more similar than DZ twins, this provides evidence of heritability
Identical twins that are reared apart share more of the same genes than fraternal twins reared
together
The Jim twins are identical twins that were given up for adoption at birth and therefore were
unaware that they had a twin. When they met, they discovered that they shared many personality
traits and behavioural habits such as favourite tv shows, using same brand of tooth paste, and
being emotionally stable
The closer the genetic relationship between individuals the stronger the correlation between their
personality traits and their level of sensation seeking
Identical twins are more alike than fraternal twins in the big-five personality traits and in
sensation seeking even when identical twins are reared apart
Adoption Studies
The correlation between adopted children and their adoptive parents which
whom they share no shared genes
If a strong correlation is found between the adopted children and their
adoptive parents then this provides strong evidence for environmental
influence on the personality trait.
Selective placement is when adoptive parents are very similar to the original
parents than this may influence the correlation between the adoptive parent
and adoptive children
Attitudes and Preferences
Wide variance in heritability of attitudes
Some attitudes (e.g., traditionalism) show high heritability (about .60), whereas others show low
or no heritability (e.g., beliefs in God)
Not clear why only some attitudes appear to be heritable
Drinking and Smoking
Behavioral manifestations of personality traits such as sensation seeking, extraversion,
neuroticism
Differences in drinking alcohol and smoking cigarettes are stable over time
Both show evidence of heritability (have to do with genetic makeup)
Shared & Non-shared Environment
Same studies that suggest moderate heritability also provide good evidence of the importance of
environmental influences
Personality characteristics show heritabilities in 30-50% range; hence,
showing substantial degree of environmentality (50-70%)
Shared: In family environment, features of the environment shared by siblings (e.g., number of
books in home, parenting)
Nonshared: In family environment, features of the environment that differ
across siblings (e.g., different friends, different teachers, parenting)
Genotype-Environment Interactions & Correlations
Genotype-Environment Interaction: When placed in the same environment, different
individuals (with different genotypes) tend to respond in unique ways.
- Entering a room with loud music
- Introverts – looking to turn down the volume
- Extraverts – looking for a dance partner
How a person reacts to a situation depends on the amount of a personality trait he/she possesses
(e.g., chocolate covered bugs)
Genotype-Environment Correlation: Individuals with different genotypes,
will have a tendency to be exposed to different environments.
The situation or activity a person selects depends on the amount of
personality trait he/she possesses (remote travel)
Three types of Genotype-Environment Correlations
Passive (You do nothing to select that environment), Reactive (the way you react
to events determine the way people react back to you), Active (seek out a
particular environment)
can be positive or negative correlations (encourage or discourage
gene expression)
Zuckerman & Kulhman – DRD4
Molecular Genetics are designed to identify the specific genes associated with
personality traits
the most frequently examined gene is DRD4
it is located on the short arm of chromosome 11- response to dopamine
The most frequently examined association between the DRD4 gene and a
personality trait has involved novelty seeking, the tendency to seek out new
experiences, especially those considered risky such as drug experiences and
risky sexual experiences
individuals with long repeat versions of the DRD4 gene were found to be
higher on novelty seeking than those with short repeats.
Personality Traits
Summaries of behavioural genetics research yield heritability estimates for major personality
traits (extraversion, agreeableness, conscientiousness, neuroticism, openness to experience) 20-
45% has to do with genetics