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Chapter 7

PSY230H5 Chapter Notes - Chapter 7: Mazda Mzr Engine, Phenylketonuria, Assortative Mating

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Ulrich Schimmack

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Personality differences can be due to following things :
Nurture differences due to env factors ( such as how parents raise their
Nature genes can contribute to personality can be influenced by
genetic variation
Behavioral genetics(indirect approach) discipline that examines the influence of environment
and genes on behavior.
molecular genetics(direct approach) studying personality on the basis of actual DNA samples
Genetic and Environmental Influences
Indirect evidence. Traditional approach based on twin, family, and adoption studies.
Direct evidence. Modern approach based on measurement of genetic markers and DNA test
Behavioral Genetics The Indirect Approach(involves twin studies)
Phenotype specific observable characteristic
Genotype information in an individuals’ DNA versions of genes are known as allels or
Environment The focus is on environment factors that vary across individuals. ( foods to
living conditions to socialization practices, education etc). contributon of env to phenotype.
population is a well- defined group of individuals.
Heritability: An estimate of the variance that individual differences in genotypes explain in
individual differences in phenotypes (h2). (amount of variance in a phenotype that is explained by
variation in thegenes that contribute to this phenotype)
Importance of two studies in behavioral genetics
Twin studies try to answer how much of the variation in a phenotype in a specific population
is due to variation in the genotype how much is due to variation in environmental factors

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Genotype nor the environment are directly measured(so they are represented as circles in the
Both are unobserved causal factors that contribute to the phenotype.
Phenotype is measurable as it is observed .
The causal effect tof the genotype on the phenotype is called heritability( h). (inherit their )
Heritability coefficient. (h2) amount of variance in a phenotype that is explained by
variation in the genes that contribute to this phenotype.
If h2 =0 then all of the variation in a phenotype is due to environmental factors.
h2 = 100% all the variation in a phenotype is due to genetic variation.
Examples of twin studies :
Monozygotic twins (MZ) genetically identical (100% genetic similarity)
Dizygotic Twins (DZ) not genetically identical 50% of their genes.
oSimilar to normal sibligs
oGood things is that they are born at the same time at the same env and are raised under
more equal environmental conditions than siblings.
Strongest Evidence for Heritability of Human Traits
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