Genetic study of dentinal growth in mandibular first molars of mice

The dentinal growth of mandibular molars of mice could be determined by genetic and environmental factors as are other quantitative characters, such as crown size and craniofacial size. To study the relative contribution of genetic and environmental factors to dentinal growth, a partial diallel cross was carried out by the mating of one pair from each of six strains of mice. In each F₁ offspring, the total amount of dentinal formation in the first molar of the right mandible was quantified as a volume by the time-marking method, using nitrilotri-acetate lead with the computerized image scanning system, and then analyzed by a quantitative genetic method. The result obtained was as follows: In either sex, both additive genetic and nonadditive genetic variance components of the accumulative volume of dentinal formation in the first molar were relatively large throughout the experimental period, while the environmental variance component was much smaller. Thus it could be concluded that the genetic factor contributed more to the whole process of dentinal growth in the first molar rather than the environmental one in this F₁ population.