Adoption studies are particularly well-suited to the study of GxE because they unambiguously separate genetic and environmental sources of variation in an outcome. Given certain assumptions2, adoptees resemble their adoptive relatives only due to shared family environmental influences, and resemble their biological relatives only due to genetic influences. For the purposes of studying GxE for alcoholism, adoption studies compare the drinking outcomes of individuals who have high versus low genetic risk, inferred from history of alcoholism in the biological parents, adopted into a range of environmental risks.
