PSY230H5 Lecture Notes - Lecture 11: Trait Theory, Molecular Genetics, Physical Attractiveness

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Published on 27 Nov 2012
Genetic and Environmental Influences
Genetic and Environmental influences on personality
Humans have different personalities according to personality measures and cross-situational consistency studies
Stability in personality over time (longitudinal studies)
Environmental factors can influence variation in personality
o i.e. parents may socialize their kids differently
Nurture- hypothesis that parents influence their children’s personality
o Alternative- genes contribute to personality
o Nature- personality traits and behaviour vary across humans could be influenced by genetic variation
across individuals
Behavioural genetics- scientific discipline that examines influence of environment and genes on behavoiur
o Most of the existing knowledge about causes of personality comes from behavioural genetics studies
Possible to study genetic influence son personality directly by getting DNA samples from people and examining
how variation in DNA across individuals related to variation in personality traits, behaviour, and life outcomes
Molecular genetics- modern approach of studying personality on basis of actual DNA samples
Most important evidence comes from studies that looked at influence of genes and environment indirectly by
comparing individuals who vary in their genetic relatedness (i.e. twin studies)
o Twin studies show that genetics have influence on personality
Behavioural Genetics- The Indirect Approach
Phenotype- variation in specific observable characteristic (i.e. eye colour)
Genotype- information in an individual’s DNA
Alleles/polymorphisms- different versions of genes
o Alleles- variations of functionally identical genetic information at same location on a chromosome (i.e.
brown, green, or blue eyes)
Environment- environment factors that vary across individuals
Population- well-defined group of individuals
o Twin studies and related studies in behavioural genetics try to answer the question of how much the
variation in a phenotype in a specific population is due to variation in genotype and how much is due to
variation in environmental factors
Neither the genotype nor environment are directly measured; unobserved causal factors that
contribute to phenotype
**causal effect of genotype on phenotype is called heritability (h)
**called heritability coefficient because we know people inherit their genes from biological
parents (square a coeffeicent for causal effect to get amount of explained variance in dependent
thus, h squared provides information about amount of variance in phenotype that is
explained by variation in genes that contribute to this phenotype
**square root of heritability effect (h squared) called heritability coefficient
0% heritability coefficient- environmental factors, 100%- genetic variation
Twin Studies
examining how similar twins are in phenotypes
Monozygotic twins (MZ) result from split of same fertilized egg during early stages of development of fetus; two
fetuses develop that are genetically identical
Dizygotic twins (DZ) result of two eggs in uterus that are fertilized by two different sperms; thus, the developing
fetuses share only 50% of their genes
o Not different from normal siblings genetically; born at same time and raised under more equal
environmental conditions that siblings
Biggest issue in twin studies is recruiting large number of MZ and DZ twins
The closer the correlation is to 1, the more similar twins are in their phenotype
Equal Environmental Assumption
Assumption that MZ and DZ twins differ only in their genetic similarity but not in similarity of environmental
factors that cause variation in phenotype
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