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Genetics and Personality

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  1. Personality Psychology Genetics and Personality

  2. Contribution of Genes or Environment • Genes rarely act completely alone • Environmental factors and other genes may modify expression • Traits can be described as • Mendelian or primarily due to a single gene • Polygenic or primarily due to multiple genes • Multifactorial or complex due to an interaction between genes and the environment

  3. Inheritance of Personality • Behavioral Genetics • Study of genetic influences on behavioral qualities, including action tendencies, personality dispositions, psychological abnormalities, and cognitive and emotional processes (the study of genetics on behavior)

  4. Goals of Behavioral Genetics • Determine the percentage of individual differences that can be attributed to genetic differences and environmental differences • Determining the ways in which genes and environment interact and correlate with each other • Figuring out precisely where in the environment the effects are taking place

  5. What is Heritability? The proportion of observed variance in a group of individuals that can be explained or “accounted for” by genetic variance.

  6. Heritability The proportion of phenotypic variance that is attributable to genotypic variance H of 20 = 20% GV and 80% Environmental

  7. Heritability Estimate • A percentage that refers to how much influence inheritance has on a trait • Used to determine how heritable different traits are • The higher the heritability estimate, the stronger the evidence that the trait is inherited

  8. Heritability Estimate

  9. Heritability Misconceptions • It can be applied to a single individual • It is constant or immutable • It is an absolutely precise statistic

  10. Behavioral Genetics Methods

  11. Behavioral Genetics Methods Adoption Studies • Examine the correlations between adopted children and their adoptive parents, or adopted children and their genetic parents • Assumptions • Representation • Placement is not selective

  12. Behavioral Genetics Methods Combination Studies • Compare MZ twins raised apart to DZ twins raised together • Compare MZ twins raised apart to MZ twins raised together

  13. Major Findings From Behavioral Genetics Research

  14. Twin StudiesJim Lewis / Springer • What does the study suggest?

  15. Jim an Jim • 37 days after birth • Romantic- love notes to wife • Son James, dog Toy, wife Linda and second wife named Betty • Woodworking (same bench in front yard) • Chevy, stock car racing, Miller Lite • Vasectomy, high blood pressure, chain smoker • migraines and nail-biting

  16. Gerald Levy and Mark NewmanSeparated at Birth

  17. Levy and Newman • Bouchard’s Minnesota Twin Study • Reunited by shared acquaintance • Upon meeting for first time: • Same mustache, sideburns, glasses • Levey: college degree in forestry- Newman planned to but worked for city trimming trees • Levey worked installing sprinker systems, Newman installed fire alarms • Both were bachelors, same taste in women • Both only drank Budweiser (pinky wrapped underneath can, crushed can afterwards) • Hunting, fishing, beach, John Wayne movies, pro-wrestling, Chinese food in wee hours • Volunteer firefighters • Both raised Jewish, neither particularly religious • When met- same remarks, at same time, same gestures- “spooky” • He is he and I am I, and we are one…

  18. Two common areas for behavioral genetics testing • Intelligence, or IQ • Personality traits such as • “Big Five” • Religiosity • Temperament • Hostility • Assertiveness • others

  19. The Big Five • Extraversion (Surgency) • Conscientiousness • Agreeableness • Neuroticism (opposite: Emotional Stability) • Openness to Experience (Intellect or Culture)

  20. Major Findings From Behavioral Genetics Research Personality Traits • Major personality traits show some modest degree of heritability • Attitudes • A substantial portion of the variance in personality traits is environmental in origin

  21. Temperament • Our emotional excitability • Temperament traits tend to remain consistent through life • Studies confirm • Genetic temperament helps form enduring personality

  22. Major Findings From Behavioral Genetics Research

  23. Major Findings From Behavioral Genetics Research

  24. Major Findings From Behavioral Genetics Research Impulsivity Individual differences in drinking and smoking habits show evidence of heritability

  25. Shared versus Non-Shared Environmental Influences The same studies that suggest moderate heritability also provide the best evidence for the importance of environmental influences

  26. Shared versus Non-Shared Environmental Influences • Shared (the presence of a TV, number of books) • Non-Shared (different friends and activities) Which environmental influence has more impact on the development of personality?

  27. Summary • Empirical evidence on heritability has become stronger over the past 2 decades • Environmental influences, especially the non-shared variety, are also important • Interactions and correlations between genetic and environmental variables can also affect personality