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

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

Heritability Coefficient (h 2 ) – 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

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

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)

Heritability coefficients change with development

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

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

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

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

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

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

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

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