Chapter 6 Learning Objectives Genetics and Personality 1 Define genome and describe the hierarchy in the genome a Genome all of our genes i The human genome contains 30 000 80 000 genes on 23 pairs of chromosomes ii Human Genome Project is designed to sequence the entire human genome i e identify the particular sequence of DNA molecules in human species but identifying sequence of DNA molecules doesn t mean identifying the function of each molecule iii Most genes in a human genome are the same for all humans b Hierarchy genome chromosomes genes DNA 2 Differentiate genotype and phenotype a Human genome i Very small number of genes differ across people including genes that indirectly code for physical traits and for personality traits 1 Genotype a trait that a person has within themselves that determines their behaviors with others a i e values likes or dislikes 2 Phenotype observable aspects of how the individual relates to the world a i e a phenotype for someone with a personality disorder is a pattern of disturbed or inappropriate relationship with others 3 Define behavioral genetics What are the controversies surrounding behavioral genetics a Behavioral genetics attempt to determine the degree to which individual differences i e personality are due to genetic and environmental factors b Controversies Ideological concerns i ii Eugenics iii Genetic determinism 1 Genes and environment interact c Knowledge is better than ignorance d Finding that a personality trait has a genetic component does not mean the environment is powerless to modify trait e Goals i Determine the percentage of individual differences in a trait that can be attributed to genetic differences and percentage that can be attributed to environmental differences ii Determine the ways in which gene and environment interact and correlate with each other to produce individual differences iii Determine precisely where in the environment environmental effects exists e g parental socialization different teachers to which children are exposed 4 What are the three major questions asked by behavioral geneticists a What causes variability in a trait genes vs environment b Which environmental effects are important e g parents teachers peers c How do genes and environment interact 5 What is heritability What is environmentality a Heritability how much an individual difference is explained by genetics b Environmentality proportion of observed variance in group of individuals attributable to environmental variance 6 Discuss three misconceptions about heritability a Heritability i CANNOT be applied to single person 1 A single individual s height for example is not 10 due to their 2 environment It is more accurate to say that the variation between people in height is 10 due to the environment ii Is NOT constant unchangeable 1 Heritability only applies to a population at one point in time 2 The more similar the environment between people the higher heritability will be Is NOT a precise statistic iii 1 Only as good as the sample used 7 List and define the four methods used in behavioral genetics Discuss some of the advantages and disadvantages of each method a Selective breeding i Can t be done ethically with humans ii Only works if a desired trait is heritable iii If selective breeding for a trait is successful the trait is at least somewhat genetic b Family studies i Correlates genetic similarity w personality similarity ii iii Problem If trait is heritable more genetic relatedness more similarity on traits 1 Families share genes and environment confounds genetic with environmental influences iv Family studies are never definitive c Twin studies i Monozygotic twins share 100 of genes ii Dizygotic twins share 50 iii Estimate heritability 1 Are identical monozygotic MZ twins more similar than fraternal 2 dizygotic DZ twins If MZ twins are more similar than DZ twins on a given trait due to heritability iv Two assumptions of twin methods 1 Equal environments assumption 2 Representativeness assumption d Adoption studies i Positive correlations on traits between adopted children and adoptive parents environmental influence ii Positive correlations between adopted children and genetic parents genetic influence iii Adoption studies are powerful because they get around the equal environments assumption genetic and environmental causes are unconfounded iv Potential problem 1 Representativeness 2 Selective placement of adopted children Ideal study v vi Twins reared apart e Twin vs Adoption Studies 1 Combines strengths of twin and adoption studies i MZ twins are MUCH more similar to each other than DZ twins ii But adopted children aren t tremendously more similar to their biological siblings than their adopted siblings iii There might be something special about having ALL your genes in common with someone iv Non additive genetic variance 8 Differentiate monozygotic and dizygotic twins a Monozygotic twins i Share a single fertilized egg a single zygote monozygotic ii Share 100 of their genes b Dizygotic twins i Come from two separately fertilized eggs two zygotes dizygotic ii Share about 50 of their genes 9 Compute the heritability estimate if I give you the correlations for monozygotic and dizygotic twins a Computing heritability quotients i Neuroticism ii DZ twins correlated at 18 iii MZ twins correlated at 41 iv Heritability 2x difference in correlation v Heritability 2 41 18 46 46 10 What is the equal environments assumption What is representativeness What is selective placement a Do twin studies eliminate problem from family studies b Equal environment assumption environment experienced by identical twins no more similar than environments shared by fraternal twins c Representativeness i Twins differ very little from non twin siblings Measured studies on the personality and intelligence of twins suggest that they have scores on these traits very similar to those of non twins d Selective Placement i If adopted children are placed with adoptive parents who are similar to their birth parents this may inflate the correlations between the adopted children and their adoptive parents In this case the resulting inflated correlations would artificially inflate estimates of environmental influence because the correlation would appear to be due to the environment provided by the adoptive parent There does not seem to be selective placement and so this potential problem is not a problem in actual studies 11 What is non additive genetic variance a The
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