Personality Chapter 6 – Genetics
- Depression and genes don’t correlate
- However, genotypes, environment, and depression do
o Stressful environment + genotype 3= depression
- Behavioral genetics: the study of the genetic and environmental contributions to individual
differences in personality and behavior
- Genes and the environment co-act together to form personality
- Personality is lemonade = sugar, lemon, and water (combination)
- Phenotype: the manifestation of the genes; the observable physical or psychological trait which
is coded by the genes.
o Phenotype= genotype + environment + gene-environment correlation + gene-
- Heritability (h ): the amount of observed individual differences in a characteristic that can be
accounted for by genetic differences.
o Across a group/population of people
o It’s like a cookie…it turns out different each time. You also can’t tell which is more
important, flour or eggs? Likewise, genetics and environment.
o Inheritance of particular trait in a particular population at a particular time
o Ex. Heritability of height can differ between different cultures/countries
- Environmentality (e ): the amount of observed individual differences in a characteristic which
can be accounted for by environmental differences.
o We see higher heritability in equalizing environments (when environments are equal.
For ex. Everyone gets the same amount of protein/meat) so the only variance that could
really exist is genetics
- Shared environment: aspects of the family environment that are generally the same for all the
children living in the same household, including physical (apartment/house), psychological
(alcohol, drug abuse, depression), and social aspects (status, education, relgion).
- Non-shared environment: aspects of the family or nonfamily environment that are unique to an
individual family member and that make him or her different from his or her siblings living in the
o Being the eldest/youngest, peers, teachers, sports, hobbies
- The importance of genetics and environments varies depending on the question (genetics,
familial environment, school environment, or personal environment)
o Finn Twin studies - Monozygotic (MZ) twins: identical twins, exact genetic duplicates of each other. MZ twins are
created when a fertilized egg, the zygote, splits into two (or more) identical parts, each of which
develops into a fetus.
- Dizygotic (DZ) twins: Fraternal twins, sharing about 50% of their genes with each other. DZ
twins are created when two different sperm fertilize two different eggs leading to the
development of genetically distinct fetuses.
- One measure of heritability: calculate correlatin
o H = 2(rmz rdz
Double the difference method (assuming same environment)
- Another way to measure heritability: compare identical twins who have been raised in separate
o MZA twins: identical twins who were separated at birth and raised in different
Ex. If both score similarly for extraversion, then you know extraversion has a
strong genetic component.
o H = rMZA
- Equal environments assumption: The assumption that identical twins are not treated more
alike than fraternal twins, an assumption behind the double-the-difference between MZ and DZ
twins reared apart measure of heritability.
o Parents don’t treat MZ twins any more alike than DZ twins
- Assumption of the representativeness: the assumption that identical twins are typical of the
population of the specific characteristic under investigation, an assumption behind the double-
the-difference between MZ and DZ twins reared apart measure of heritability.
o Ex. Twins are often premature so you can’t include them in studies where you’re looking
at prematurity (because they are more likely)
- Selective placement: the assumption that adopted families of MZ twins raised apart are
different from each other, that the identical twins were not purposely placed in similar
environments, an assumption behind the r mzameasure of heritability.
o They could be placed in similar families and therefore adopt similar personalities = you
won’t be able to tell how much genetics play a role and how much environment does
- Both, assumption of the representativeness and selective placement aren’t usually problems in
- There are true experiments (there is an independent and dependent variable) and there are
correlational experiments (just look at the relation)
- Observed differences in personality traits = 40% genetics + 0% shared environment + 40% non-
shared environment + 20% error
- Heritability of personality traits ranges from 0.40-0.60
- Identical twins are very similar in the 5 factor traits even if they are raised apart - Identical twins have the highest correlations
- A lot of personality is influenced by non-shared environments
- When we rate ourselves, we tend to say genetics play a more important role in personality
o Founder of modern genetics
o Pea plant experiment
o Found that next generation had more smooth plants than wrinkly
Each parent passes one form of a gene to the offspring (so offspring has 2 forms
of the same gene like smooth and wrinkly)
Alleles: alternative forms of the same gene which occur in pairs, one inherited
from each birth parent.
They can either be the same (smooth and smooth) or different (smooth
and wrinkly) but one will be dominant over the other
Mendelian inheritance: a pattern of inheritance nam