2,3,7,8-Tetrachlorodibenzo-p-dioxin affects fluctuating asymmetry of molar shape in mice, and an epistatic interaction of two genes for molar size

Fluctuating asymmetry (FA), random variation between left and right sides in a bilaterally symmetrical character, is a commonly used measure of developmental instability that is expected to increase with increasing environmental stress. One potential stressor is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a powerful toxicant known to disturb tooth development. In this study, mice in the F(2) generation produced from an intercross between two inbred strains (C57BL/6J and AKR/J) were exposed in utero to TCDD. We hypothesized that TCDD would increase FA in the molars of exposed mice over that of the control mice. In addition, we hypothesized that we would discover genes for molar size, shape or asymmetry whose expression would be affected by TCDD. We detected a very small, but significant, increase in FA of molar shape (but not size) in the TCDD-exposed mice compared to the control mice, although molar size and shape did not differ between these groups. Although we did not uncover any genes that acted differently in the TCDD exposed and control groups, we did identify two genes whose dominance by additive epistatic effect on molar size was affected by TCDD. We concluded that although TCDD may be affecting the expression of some genes governing the development of molars in our population of mice, FA of molar size and shape is not a particularly sensitive indicator of this effect.