Figure 1: Sex-limitation model for adolescent depressive symptoms. The magnitude of additive genetic (), shared environmental (), and nonshared environmental () influences may differ for males and females (am ≠ af, cm ≠ cf, and em ≠ ef), and/or the genetic () or shared environmental () correlation among opposite-sex twins may fall below the expected genetic (.50) and shared environmental (1.00) correlations for same-sex dizygotic twins.