Answer to Question 1
Familial association studies involve an analysis of shared traits or disorders among family members based on their degree of kinship, or relation. For example, in examining a family tree, one might discover that the more closely related people are, the more likely they are to have a particular trait. These studies provide supportive evidence of genetic contributions to traits or disorders. Twin studies involve the analysis of difference in the rates of overlap (or concordance) for a given trait or disorder between identical and fraternal twins. These studies provide strong evidence of genetic factors when concordance rates are higher among identical than fraternal twins. Adoptee studies involve the analysis of similarity in traits or disorders between adoptees and their biological and adoptive parents or between identical twins raised apart versus together. This is the clearest way to establish the role of heredity versus environment. If concordance is greater with traits or disorders exhibited by the adoptive parents, environmental influences are indicated. If concordance is greater with traits or disorders exhibited by the biological parents, genetic factors are indicated. These studies may not control for the effects of common environmental factors, such as shared environments shortly after birth or ongoing relationships between the twins.
Answer to Question 2
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