Genetic and environmental factors in the longitudinal growth of rats: II. Ventrodorsal craniofacial size.

By means of roentgenographic cephalometry and quantitative genetic analysis, the relative contribution of the genetic and environmental components to the ontogenic change of the ventrodorsal view of the craniofacial complex was shown to vary with age. The genetic component of variance significantly increased until the 80th day. Inversely, the maternal component of variance showed a large value during the early stage of postnatal growth and gradually decreased thereafter to a very small amount by the 80th day. In general, it appeared that the genetic effect became larger with the age of the rat and the maternal effects tended to diminish. The environmental component of variance did not change much over the course of the experiment. We thus concluded that the genetic effect contributed to the change of the ontogenic variation of the craniofacial complex through all experimental periods and the maternal effect contributed to the change at the early growth stage of the craniofacial complex.