AHR and cleft palate: A study on the mechanism of TCDD toxicity found that 100% of fetuses exposed to a specific concentration of TCDD at 12.5 days of fetal life developed cleft palate; however, when the same concentration of TCDD was administered to knockout mice, no cleft palate developed, suggesting that the presence of aryl hydrocarbon receptor (AhR) is important for the development of cleft palate via TCDD exposure during the fetal period [31].