FIGURE 1. A Schematic Description of the Triparental Family Design^a.

^aTriparental families contain three parents. The biological mother who raises the child contributes both genes (G) and rearing environment (E) to the offspring. The biological or not-lived-with father never resides with or near the offspring and therefore contributes, as a first approximation, only genes (G) to the offspring. The stepfather, who is not biologically related to the offspring, contributes only rearing environment (E).