Genetics and Personality

1. Genetics and Personality Heritability and Individual Differences

2. What is inherited? Extraversion? Neuroticism? Depression? Alcoholism?

3. Traits are NOT inherited Only genes are inherited Genotype – Genes Phenotype – Traits

4. The Human Genome • Contains between 30,000 and 40,000 genes • All are located on 23 pairs of chromosomes • The body contains roughly 100 trillion copies of the human genome • The Human Genome Project

5. No one-to-one relationship between genotype and phenotype Different genotypes → Same phenotype Same genotype → Different phenotype Context (other genes, cellular, etc.) is critical No specific genetic markers for personality

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

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

9. What is 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 Selective Breeding

11. Maze Running in Rats Thompson Assess rat ability to traverse maze Designate rats as maze-bright or maze dull based on performance Breed maze-bright with maze-bright and maze-dull with maze dull Assess maze running ability Maze bright strain far superior to maze dull strain

12. But what about environment? Cooper and Zubek Simultaneously manipulate genes and environment Genes: Obtain offspring of maze-bright and maze-dull strain Environment: Raise in normal, enriched, impoverished environment

13. Maze errors (Cooper & Zubek)

14. Gene X Environment Interaction Genes matter in some environments but not others Environment can override effects of genes

15. Behavioral Genetics Methods Twin Studies • Monozygotic Twins (100% shared genes) • Dizygotic Twins (50% shared genes) • If MZ twins are more similar than DZ twins, this provides evidence of heritability Heritability = 2(rmz – rdz)

16. Temperament – Buss & Plomin

17. Heritability of Complex Behaviors

18. Heritability of Self-Monitoring

19. Misc. Heritability Estimates Trait h2 Height .80 Weight .60 IQ .50 Conservatism .30 Religiosity .16 TVviewing .20

20. Two Issues for Twin Studies • 1. Are the results valid? Do twin studies overestimate heritability? • 2. What are the mechanisms that explain heritability, especially complex behaviors?

21. Validity Issues Generalizability– Small, self-selected, samples Biased Ratings – Influenced by expectations

22. Validity Issues MX:DZ ratio > 2:1 (Note: genetic ratio is 2:1) Possible reasons: 1. Environment MZ treated more similarly MZ interact more frequently 2. Genetic nonadditivity

23. Alternative to Twin Studies Twin studies with additional controls Adoption studies Twin/Adoption studies

24. Twin study with controls; Rose et al Sweden – use twin registry Measure: I, E (from Eysenck), Interaction Frequency Results: MZ > DZ for I, E, and Interaction Frequency MZ > DZ for I, E, controlling for Interaction Frequency

25. Adoption Results – Loehlin et al.

26. Twin/Adoption Method – Sample Results MZ Twins DZ Twins ApartTogetherApartTogether Extraversion .30 .54 .04 .06 Introversion.25 .41 .28 .24 Openness .43 .51 .23 .14 Conscientiousness .15 .41 .03 .23 Agreeableness .19 .47 .10 .11 Emotionality.37.49.04.08 Activity.27.38 .00.18 Sociability.20.35 .19 .19 Mean .27 .44 .11 .15

27. Explanations for Heritability Many demonstrations of heritability, even for complex traits (e.g., crime) No gene(s) for complex phenotypes How can they be inherited?

28. Gene X Environment Interaction Genotype High Emotionality High Activity Ignored Punished Low self-esteem Aggressive Delinquency Phenotype Crime

29. Types of Interaction/Correlation • Selective Exposure – Genes influence types of environment to which one is exposed • Differential Susceptibility – Genes influence how one reacts to environment