Figure 1.

Path model for the influences on mannan-binding lectin (MBL) or lung surfactant protein D (SP-D) in twins. The influences are divided into additive factors (A), genetic dominance factors (D), and shared (C) and non-shared (E) environmental factors. Additive genetic factors and genetic dominance factors are both perfectly correlated in monozygotic (MZ) twins, whereas in dizygotic (DZ) twins the correlation between additive genetic factors equals one-half and the correlation between genetic dominance factors equals one-quarter.