The experiments herein reported were undertaken to test whether a selected teratogen that can cause anomalies in 95 percent of fetuses can also cause chromosomal anomalies. 6-Amino nicotinamide was selected as the teratogenic agent, cleft palate as the deformity to be induced, and pregnant outbred females of the 15year-old Phipps mouse colony as the biologic model to be used in the experiments. This agent, this defect, and this animal were chosen because much work had been done on chemical, morphologic, and embryological aspects of all three variables (1).Pilot studies were made to establish the critical period for production of cleft palate by 6-amino nicotinamide in offspring of pregnant females of the Phipps mouse colony. Standard methods were modified and applied for the demonstration of chromosomal structure of cells of tissues adjacent to and remote from palatal defects induced by the administration of 6-amino nicotinamide to pregnant females around the 13th day of gestation. Chromosomal analyses were also carried out on maternal bone marrow, a tissue regularly in a high state of mitotic activity, to determine whether or not 6-amino nicotinamide injection had any pathogenic effect on maternal chromosomal patterns. For purposes of comparison similar studies were made of chromosomal patterns in cells of
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