Age trends in transmissible and non-transmissible components of family resemblance for stature

Yearly measurements of recumbent length and stature on participants in the Fels Longitudinal Study of Growth and their first-degree relatives were submitted to path analysis. Using a model consistent with simple polygenic inheritance, two parameters were estimated at each age: t2 or transmissibility, and s, or non-transmissible sibling resemblance. Transmissibility showed no long-term age trends, whereas non-transmissible sibling resemblance declined steadily from age four years to the late teens. The factors controlling family resemblance for stature (genes and common family environment) make different contributions at different points in the growth cycle of these family members. These differences are more discernable in the Fels data because all family members, including parents, are measured at the same age throughout childhood.