Chapter 6 – Genetics Behavioral Genetics - The study of the genetic and environmental contributions to individual differences in personality and behavior- Haeffal et al. (2008) studied adolescent boys in Russia in a juvenile detention centero Looked at stressful environment (measured by maternal rejection), and incidence of clinical depression, as well as genotypes (1, 2, or 3) o Findings demonstrated an increase in clinical depression ONLY in those adolescents who had maternal rejection and genotype 3  Direct effect on our behavior w/ experiences of maternal rejection  Direct effect of gene and environment Nature and Nurture Together- Personality is a combination of botho Genetic o Culturalo Familial o Idiosyncratic learning experiences (unique to you)- Genes and environment 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) o A genotype responds differently to an environment (ex: Russian study)- Genotype-environment correlation – may be impossible to separate the effects of genes from the effect of the environment (genotype is exposed differently to an environment) - Phenotype – what the heredity produceso Phenotype = genotype + environment + gene-environment correlation+ gene-environment interaction Heritability - Heritability (h^2): amount of observed individual difference in some characteristic that can be accounted for by genetic differenceso Refers to specific differences across a group or population of people (not to a specific person) Ex: the heritability of height is 80%, 20% due to environmentaldifferences + some % of measurement erroro Particular trait in a particular population at a particular time Ex: 80% or more in US vs. only 65% in China & western Africao Estimate that refers to a specific population Environmentality - Environmentality (e^2): extent to which observed individual differences can be traced to individual environmental differenceso Ex: what effect does environmentality have on height? Underdeveloped countries have less access to nutrition, affecting height o Lower e^2 estimate in equalizing environments (environments that are the same for everyone) and higher estimates in more variable environments  Access to resources in rich environments = smaller effect environment can have - Higher heritability in developed countries (US) Shared Environment - Environment refers to any part of the phenotype not accounted for by genes- Shared = aspects of the family environment that are generally the same for allchildren in a householdo Physical = type of dwelling, layout, things in the home o Psychological = parenting practices, psychopathology, quality of sibling interactionso Social aspects = SES, family structure, urban or rural setting, religion Nonshared environment- Experiences that relatives have which make them different from one another o Birth ordero Differential parental treatmento Peers, hobbies, sports, teachers- In regards to personality, most of the environmental influence tends to be nonsharedo Think about you childhood experiences shared by a sibling, did you both react the same way?Environment Cont.- It may be that family environment makes children “different”o Parents treat children differently based on their personalities, creatinga unique environment for each child- Or, researchers are looking too broadlyo Missing specific aspects of the environment that are shared Ex: sense of humor, etc.Finn Twin Studies- Wanted to estimate the separate effects of genetics (comparing identical and non-identical twins), familial environments (twins and matched control classmates), nonfamilial environments (control kids from same class to one another), and personal environment (kids from different neighborhoods to one another)o Behaviors studied included self-report of cigarette smoking, saying prayers, drinking - Genetics did not explain total variance- Greater effect of shared environment for smoking, drinking, saying prayers, getting drunk- Neighborhood – drinking without peers- Personal environment – participating in church activities Estimating Heritability - Do people who have similar genes show similar characteristics?- If a characteristic has a strong genetic component then we would expect who to be more similar than strangers in that characteristic?o Most of gene studies are with twins - Identical twins share 100% of genes- 50% - parents, siblings, fraternal twins- 25% - grandparents, aunts, uncles, double cousins, half-siblings, nieces, and nephews- 12.5% - great grandparents, first cousins, great aunts & uncles - Identical twins – monozygotic (MZ) - Fraternal twins – dizygotic (DZ) - One measure of heritability is to calculate the correlation (r) between twins on given trait and compare the correlation between MZ and DZ twins- Comparison of twins between MZ and DZ twins raised together: h^2=2(rMZ-rDZ) - Comparison of MZ twins raised in separated environments: h^2=rMZAo Correlation between the two twins separately - Methods and assumptions when utilizing twinso Double-the-difference method – assumes that twins were reared under equal environments  If they are treated more similarly, may artificially inflate the estimate, so environmental effect (similar treatment) may be mislabeled as a genetic effect (similar personality) o Equal environments assumption – applies only to similar treatment that is related to the specific characteristic under study  Dressing twins alike and then measuring fashion sense vs. shynesso Assumption or representativeness – assumes that twins are typical of the population  Possible effect of prematurity or low birth weight - Limitations of twin studies reared apart o Selectiveness – assumes the adoptive families are different o Representativeness – assumes that people who adopt are different than people who do not Heritability of Common Personality Characteristics - All individual differences in human behavior are moderately heritable o Cognitive abilities, personality, social attitudes, psychological interestsand psychopathology Heritability and Personality - Ranges from .40 to .60 and is the same for men and women - Shared environments account for very little variation- Nonshared environments account for a great deal- Variance in personality traits o Observed differences in personality traits = 40% genetics + 0%