Which research design is used to explore genetic influence by comparing different types of twins, including identical and fraternal twins?

• A. Case studies
• B. Twin studies comparing identical and fraternal twins
• C. Cross-sectional studies
• D. Longitudinal studies

Answer: (B)

Twin studies compare identical twins who share almost all their genes with fraternal twins who share about half, providing a direct way to separate genetic and environmental influences on a trait. If a trait is strongly genetic, identical twins should resemble each other more than fraternal twins, because their greater genetic similarity increases the chance both will express the trait. By looking at how often both twins show the trait (concordance), researchers can estimate how much genetics contribute to variation. The other designs don’t exploit this comparison of different levels of genetic relatedness: case studies focus on individuals in depth, cross-sectional studies examine different people at one point in time, and longitudinal studies follow the same people over time. Twin comparisons uniquely reveal genetic influence through the contrast between identical and fraternal twins.