Abstract
Teeth, maxilla and mandible are complex structures and their sizes can be determined by genetic and environmental factors. The purpose of this study was to investigate the relationship between genetic factors in the growth of crowns and jaws in inbred mice. We measured the mesiodistal crown diameters of the first molars, anteroposterior mandible length between menton to gonion and anteroposterior maxilla length between the anterior border of the incisor pore and the posterior border of the basisphenoid in 21 SMXA recombinant inbred (RI) strains and their parental strains, SM/J and A/J.
The results obtained were as follows.
1. Continuous distribution patterns of both crown diameters in the first molars and lengths of jaws in SMXA RI strains suggest that sizes of the crowns and jaws are not determined by a simple Mendelian inheritance and are controlled by multiple genes.
2. Crown diameters in the first molars and lengths of jaws in SMXA RI strains may be strictly controlled by genetic factors rather than environmental factors.
3. It is conceivable that SM/J and A/J-derived alleles include both increasing and decreasing effects on the growth of the crowns and jaws, and that the sizes of the crowns and jaws in SMXA RI strains are determined by a combination of SM/J and A/J-derived alleles.
4. A correlation of crown diameters between the upper and the lower first molars suggests that the same gene effects influence crown growths of both the upper and the lower first molars.
5. As maxilla and mandible lengths have a mutual relationship, the same gene effects may influence the growth of both the maxilla and mandible.
6. There was no correlation between the maxilla length and crown diameters of the upper first molar. There was also no correlation between the mandible length and crown diameters of the lower first molar. These findings suggest that crown and jaw growths are genetically independent, and that different gene effects strongly influence crown and jaw sizes.
