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Chapter 4 Genetics and Personality

Personality Psychology. Chapter 4 Genetics and Personality. Biological Domain. Key Assumptions of the Biological Paradigm Physical elements and biological systems within our bodies can influence or be influenced by our behaviors, thoughts, and feelings (Physiological Perspective – ch. 3)

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Chapter 4 Genetics and Personality

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  1. Personality Psychology Chapter 4 Genetics and Personality

  2. Biological Domain Key Assumptions of the Biological Paradigm • Physical elements and biological systems within our bodies can influence or be influenced by our behaviors, thoughts, and feelings (Physiological Perspective – ch. 3) • Personality characteristics are under genetic influence (Genetic Perspective – ch. 4)

  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 • Other definitions: • The index of genetic influence on personality • The amount of variance accounted for by inheritance for the trait under study • The higher the heritability estimate, the stronger the evidence that the trait is inherited

  8. Heritability Estimate Heritability = 2(rmz – rdz) Heritability of Height = 2(.93 - .48) = .90

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

  10. Heritability Nature-nurture debate • At the level of a single individual, there is no debate • At the level of a population, we can begin to disentangle the influence of genes and environments

  11. Behavioral Genetics Methods Twin Studies • Monozygotic Twins (100% shared genes) • Dizygotic Twins (50% shared genes) • Assumptions • Equal environments assumption • Representation assumption

  12. 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

  13. 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

  14. Major Findings From Behavioral Genetics Research • Personality Traits • Temperament • Impulsivity • Intelligence

  15. 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

  16. Major Findings From Behavioral Genetics Research

  17. Major Findings From Behavioral Genetics Research Temperament • A person’s overall “emotional nature” • Definition • Buss and Plomin’s “Temperaments”

  18. Major Findings From Behavioral Genetics Research

  19. Major Findings From Behavioral Genetics Research

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

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

  22. 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?

  23. Genes and the Environment • Genotype-Environment Interaction • Genotype-Environment Correlation • Passive • Reactive • Active

  24. Molecular Behavior Genetics The attempt to identify the specific genes associated with personality traits • D4DR and “novelty seeking”

  25. Behavior Genetics, Science, Politics, and Values • Political goals? • Excuse for behavior? • Should science and values be separated? • Is science ever objective?

  26. 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

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