<prompt> Chromosomal non - disjunction responsible for all except?Downs syndromeNeurofibromatsis type 1Pradderwilli syndromeAngleman syndrome  <response>: Ans. is b i.e., Neurofibromatosis type 1Nondisjunction Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division.There are threeforms of nondisjunction: Failure of a pair of homologous chromosomes to separate in meiosisFailure of sister chromatids to separate during meiosis II, andFailure of sister chromatids to separate during mitosis. 