PSYC 2740 Lecture Notes - Monoamine Oxidase, Gender Dysphoria, Twin Study

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Published on 14 Apr 2013
School
University of Guelph
Department
Psychology
Course
PSYC 2740
Professor
1
PSYC*2740-01
January 30, 2013
The Biological Domain: Genetics & Personality
Genes and Personality: Issues and Controversy
Why might the study of genes and personality be controversial?
1) Ideology: the fear that if we do establish genes that affect certain personality
factors, then genes might be used to explain everything or people will not use
genes to explain any of the factor. People are also afraid that police systems
will be driven to base a lot of their information on genetics. Therefore,
political agendas might be driven by these findings.
2) Eugenetics: the controversy regarding using eugenetics to knockout specific
traits.
Percent of Variance: There are differences between people due to a certain cause
(in percentages). Many times this is used to look at what percentage of a personality
trait is a product of genetics or the environment. These percentages are not concrete
however, there might be errors or differences between different studies.
Heritability vs. Environmentality
Heritability: amount of phenotypic variance in a group due to genotypic variance.
Genotypic variance: individual differences in people’s genes.
Environmentality: amount of observed variance due to the environment.
Behavioural genetics methodologies
Family studies
If personality traits are heritable, you should see personality traits across
generations of a family. In family studies, you examine correlations between genetic
relatedness of family members and personality similarity.
Within families, there is a percent of shared genes. Between parents and children,
and children and their siblings, there is 50% shared genes. Between grandparents
and grandchildren, there is 25%. Closer relatives should have more personality
similarity.
Twin studies
In twin studies, we look at monozygotic and dizygotic twins. We estimate
heritability via the similarity of monozygotic versus dizygotic twins. We use the
heritability formula (which is the difference between the correlations between),
which is
Heritability (squared) = 2(rmz rdz), where rmz = correlation between
monozygotic twins for a trait, and rdz = correlation between dizygotic twins for a
trait.
When we make predictions based on findings from twin studies, we must make
some critical assumptions. First, we assume equal environments for both
monozygotic and dizygotic twins. Although there will be some differences in even
the way parents treat different kinds of twins, there usually won’t be a difference
that would meaningfully impact the results of these studies. Another critical
assumption is that the twins should be a representative of the general population.
Adoption Studies
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2
In adoption studies, we examine the correlations between adopted children and
adoptive parents. We can also get information from the birth parents and look at the
correlations between the children and their adoptive parents, and the children and
their birth parents. We compare these two correlations to see how
environmentability and heritability has affected these children.
Some limitations of adoption studies are that we make an assumption of
representativeness, but the question is whether the children and parents represent
the general population? The other limitation is selective placement, which is when
adoptive children are placed with parents similar to their birth parents. Luckily, this
has not been a major issue and is unlikely to happen, however, we must look at the
limitations as well.
Twins Raised Apart
This method combines the strengths of twin and adoption studies where heredity is
equal to the correlation of the trait between the twins.
Major Findings: Big 5 Traits
The Big Five is a general trend found across many different studies. The Big Five is
found to have a moderate heritability of about .50. This tells us that on the one hand,
heritability does play a role, but it also means that environment plays an additional
role.
Major Findings: Divorce
Divorce is found to be higher in monozygotic versus dizygotic twins (suggests that
divorce is partially genetic)
About fifty percent of the variance in divorce is due to genetic influence. Divorce
stems from traits that partners bring to a marriage (the traits that each person bring
to the relationship are more important).
Major Findings: Smoking and Drinking
Neuroticism (these behaviours may be used to reduce levels of anxiety),
extraversion (is a social thing, people drink and smoke in a social setting), and
sensation seeking are all associated with smoking and drinking. There is moderate
heritability for smoking and drinking habits, however, there is more heritability for
alcoholism versus daily drinking habits. This is consistent across sexes.
Major Findings: Gender Identity Disorder (GID)
Diagnosis:
1) Cross-gender identification
2) Psychological discomfort with one’s biological sex
Gender Identity is quite heritable (.62). There is speculation about it being
neurological.
People with this diagnosis are really susceptible to depression, victimization, and
anxiety. There is also still controversy regarding it being a diagnosis.
Shared vs. Nonshared Environmental Influences
Generally, non-shared experiences and environments yield the differences in
personalities, rather than shared environmental influences.
Analyzing How Genes and Environment Interact
Genotype-environment Interaction
The main thing that needs to be analyzed here is when you have a differential
response of individuals with different genotypes to similar environments.
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Document Summary

People are also afraid that police systems will be driven to base a lot of their information on genetics. Therefore, political agendas might be driven by these findings: eugenetics: the controversy regarding using eugenetics to knockout specific traits. Percent of variance: there are differences between people due to a certain cause (in percentages). Many times this is used to look at what percentage of a personality trait is a product of genetics or the environment. These percentages are not concrete however, there might be errors or differences between different studies. Heritability: amount of phenotypic variance in a group due to genotypic variance. Environmentality: amount of observed variance due to the environment. If personality traits are heritable, you should see personality traits across generations of a family. In family studies, you examine correlations between genetic relatedness of family members and personality similarity. Within families, there is a percent of shared genes.

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