Over 5 of human babies born have recognizable malformations some of them mild some of them severe. Some birth defects are produced by mutant genes or chromosomal abnormalities, while others are produced by environmental factors Genetic defects: malformations often appear as syndromes Use of animal models to identify genetic, cellular and molecular basis of human syndromes Environmental defects: disruptions Responsible agents: teratogens-chemicals, viruses, radiationOver 5 % of human babies born have recognizable malformations, some of them mild some of them severe. Some birth defects are produced by mutant genes or chromosomal abnormalities, while others are produced by environmental factors. Genetic defects: malformations – often appear as syndromes Use of animal models to identify genetic, cellular and molecular basis of human syndromes. Environmental defects: disruptions Responsible agents: teratogens – chemicals, viruses, radiation