CHAPTER 6.docx

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University of Toronto Scarborough
Connie Boudens

CHAPTER 6: GENETICS - Genotypes: specific gene combinations - Behaviour Genetics: study of the genetic and environmental contributions to individual differences in personality and behaviour Nature and Nurture as Allies - Human behaviour and personality is an inextricable combination of both genetics and environment - Nature and nurture transact (can work separately, together or may influence one another) - Genotype-Environment Interaction: Certain environments have different effects on people depending on their specific genetic makeup (genotype responds differently to an environment) - Genotype-Environment Correlation: It may be impossible to separate effects of genes from effects of environment (genotype is exposed differently to an environment) - Phenotype: = Genotype + Environment + Interaction + Correlation Genes and Environment as Co-Actors Heritability - Heritability: amount of observed individual differences in some characteristic that can be accounted for by genetic differences (refers to differences across population/group, not a specific person) - Impossible to say how much your height is due to your genes but given a group we can say about 80% of height differences is due to differing genes - Heritability refers to the inheritance of a particular trait in a particular population at a particular time (so they can differ based on researcher and methods and time) Environmentality - Environmentality: amount of variance in personality accounted for by the environment - We see higher heritability in equalizing environments (environments that are the same for everyone) Shared and Non-Shared Environments - Shared Environment: aspects of the family environment that are generally the same for all children in the household - Non-Shared Environment: experiences that relatives have which make them different from one another - When family members resemble each other, it is more often due to heredity than shared environment Estimating Heritability - One measure of heritability is to calculate the correlation between twins on a given trait and compare the correlation between MZ and DZ twins (h = 2(r -r )) mz dz - Second way of estimating heritability is to compare identical twins who have been raised in separate environments (MZA twins) h = r 2 MZA - Double-the-difference method assume that twins were reared under equal environmental conditions - If MZ twins are treated more alike, that shared environmental factor could inflate heritability - Equal Environments Assumption: applies only to similar treatment that is related to specific characteristic under study (assuming the environments are equal) - Assumption of Representativeness: double-the-differences assumes twins are typical of a population - The rMZA has limitations – assumes adopted families of each twin are different from each other. If they are alike, may increase similarity between twins, inflating heritability - Selective Placement: selectively placing twins when they are being adopted to be in similar families. This makes the genetic and environmental effects inseparable - RMZA studies also assume that families that adopt are the same as families who do not - If adopted children are more similar to their birth parents than their adopted parents we can assume a higher genetic component Heritability of Common Personality Characteristics - Heritability of personality traits range from .4-.6 and is same for both men and women - Observed differences in personality traits = 40% genetics + 0% shared environment + 40% non-shared environment + 20% error - Heritability of all 5 Factors is in the .41-.50 range - Environment (shared and non-shared) acc
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