Chapter 6: Genetics & Personality
January 31 2012
Genes & Personality: Issues and Controversies
Ideology: many people worry that findings from behavioral genetics will be used to
support particular political agendas.
i.e. if individual differences in thrill seeking are caused by specific genes then does
this mean that we should not hold juvenile delinquents responsible for stealing cars
for joy rides.
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.
- Certain people would not be allowed to reproduce
- Fear of a “master race”.
Percentage of Variance: refers to the fact that individuals vary, or are different
from each other, and this variability can be partitioned into percentages that are due
to different causes (Genetics and Environment)
- Is a statistic that refers to the proportion of observed variance in a group of
individuals that can be accounted for by genetic variance. (Amount of
phenotypic variance in a group due to genotypic variance)
- Provides useful information in identifying the genetic and environmental
determinants of personality.
Phenotypic Variance: refers to observed individual differences, such as height,
weight, or personality.
Genotypic Variance: refers to individual differences in the total collection of genes
possessed by each person.
Environmentality: Amount of observed variance due to environment (non-genetic)
Behavioral Genetic Methods
- 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. Twin Studies:
- Estimate heritability by gauging whether identical twins, who share 100
percent of their genes, are more similar to each other than are fraternal
twins, who share only 50 percent of their genes.
Monozygotic (MZ) Twins: are identical twins, come from a single fertilized egg, which
divides into two at some point during gestation. They share 100 % of their genes.
Dizygotic (DZ) Twins: not genetically identical, only share 50 % of genes, come from
2 eggs that were fertilized separately.
Equal environments Environments for MZ twins NO different vs. DZ twins
Non-representativeness Twins should be representative of general population
- Most powe