As described in the text, radiation and chemicals in the environment can induce mutations in cells. Why do the random mutations induced by the environment NOT violate or negate the results of the Lederberg's experiments

Can happen anywhere along the spine if the neural tube does not close all the way. the backbone that protects the spinal cord does not form and close as it should. this often results in damage to the spinal cord and nerves. a) cleft palate b) spina bifida c) encephalocele d) down's syndrome