Medical Genetics (3)Chromosome non-disjunction The failure of a pair of homologous chromosomes to separate properly during meiosis. The failure of homologues(at meiosis) or sister chromatids(at mitosis) to separate properly to opposite poles, that is two chromosomes or chromatids go to one pole and none to the otherMedical Genetics (3) Chromosome non-disjunction The failure of a pair of homologous chromosomes to separate properly during meiosis. The failure of homologues (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles, that is two chromosomes or chromatids go to one pole and none to the other