Family/Kinship Studies Compare individuals with different degrees of genetic relatedness on a specific characteristic or

1. Family/Kinship Studies • Compare individuals with different degrees of genetic relatedness on a specific characteristic or behavior • Exs: adoption studies, twin studies

2. Twin Studies: • Compare identical twins to fraternal twins on a particular characteristic/behavior • Identical twins share 100% of their genes and fraternal twins share 50% of their genes • If (as a group) identical twins are more similar than fraternal twins, assumed that genes influence the characteristic

3. Heritability Coefficient (h2) • Estimates the proportion of variability in individual characteristics that is due to genetic differences • Ranges from 0 to 1 • Ex: A heritability coefficient of .60 indicates that 60% of the measured variation in a specific characteristic is due to genetic differences in the sample • Can estimate environmental influences using comparable statistics

4. Interpretation of Heritability Coefficients • Apply to populations (groups), not individuals • Correct: 50% of the variation in IQ in a specific sample is due to genetic differences • Incorrect: 50% of an individual’s IQ is due to their genes

5. Heritability coefficients reflect genetic and environmental diversity • Variability in a specific characteristic is due to genetic and environmental influences • G + E = 100% of the variability • The more environments vary, the lower heritability estimates will be (and vice versa)

6. Heritability coefficients change with development

7. Heritability coefficients are specific to a particular sample in a specific environment at a single point in time

8. Characteristics that are heritable can be modified by environmental influences • Heritability coefficients do not indicate lack of malleability

9. Shared and Non-Shared Environmental Effects • Behavioral genetics research allows estimation of two types of environmental effects • Shared: Environmental influences that make individuals similar in a common environment • Non-shared: Environmental influences that make individuals different in a common environment

10. General Criticisms of Heritability Estimates • Not useful because they cannot be generalized across samples and will change if environments change • Not useful because they tell us nothing about specific genetic and environmental influences

11. General Criticisms of Behavioral Genetics Research Designs • Attempt to partition variance attributable to genes and environment—assume independence • Gene-environment correlations? • Failure to take into account gene-environment interactions • Even if g-e interactions are tested, most studies have insufficient power to detect them

12. Gene-Environment Correlations Passive G-E Correlations • Parents provide environments for children that are influenced by their own genes • Because the child’s genes are correlated with parents’ genes, the child’s genes are correlated with the environment that parents provide • The environment the child experiences is correlated with his/her genes

13. Evocative G-E Correlations • Children evoke or elicit responses from others that are influenced by the child's genes • Children’s environments are correlated with their genes

14. Active G-E Correlations • Children (and adults) seek out environments that are compatible with their genes (niche-picking)   • Environments children choose are correlated with their genes