PSYC 100 Study Guide - Heritability, Random Effects Model, Human Genome Project

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11 Apr 2013
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Week Seven: Heritability and Evolution
What are the evolutionary underpinnings of behaviour
Genetics
What is the relationship between genes, heredity, and behaviour
Developmental Psychology: concerned with the environmental variance component, that is, the prenatal
and postnatal environmental influences affecting individuals during their lifetimes
Evolutionary Psychology: concerned with design of human nature, all human behavioural characteristics
that are the product of natural selection in ancestral environments
Behavioural Genetics: concerned with the partition of individual differences into genetic and
environmental variance components
Genetics Review:
Our genetic material, or DNA, is organized into structures called chromosomes that are located in
the nucleus of every cell; genes are regions of chromosomes that encode particular proteins
The same genes can be expressed differently depending on interactions with the environment
Much of our understanding of gene’s effects on behaviour come from twin studies, however it is
still sometimes difficult to separate genetic and environmental influences
Heritability Review:
Genetic influence is measured by a statistic called the heritability coefficient, or h2
Heritability is the proportion of observed variance in behaviour that can be attributed to genetic
differences among individuals it is population specific
E.g. any differences between identical twins will have a heritability of zero since genes are not a
factor, whereas any differences between a homeschooled household of adopted children with
have very high heritability because the children have such similar environments but not genes
Genes and Disorders
One Gene, One Disorder (OGOD) Hypothesis: theorize that one gene is responsible for one
disorder, or a single specific gene is the causal agent in a specific disorder (popular until recently)
Pedigree Studies: studies follow several generations of families, studying inherited traits/genes
Unfortunately, pedigree studies and the OGOD strategy have not been successful in the area of
major mental disorders because the etiology of the disorders does not involve single genes of
large effect, instead many genes are involved they are polygenic
Focus is now on alleles, and The Human Genome Project (which compares people regardless of
the kinship status) has allowed for the identification of many markers/chromosomes
Variance and Competition
Genes that increase an offspring’s chances of survival (give additive variance) will become more
common in the population (have increased gene dosage) until they no longer add survival value,
while genes that do not affect survival (have non-additive variance) will continue to vary
Change in Evolutionary Fitness (probability that the line of descent from an individual with a
specific trait will not die out) requires additive genetic variance, genetic variance due to gene
dosage, as opposed to interactions among different genes (non-additive variance)
When the population reaches maximal fitness, the additive genetic variance is zero (fixation)
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