Practice question

Non-disjunction describes error during cell division where homologous chromosomes in meiosis I or sister chromatids in meiosis II or mitosis fail to separate properly, both copies moving same spindle pole due defective cohesin cleavage, spindle assembly checkpoint failure, or merotelic kinetochore attachment lacking correction. Result two daughter cells aneuploid one with n+1 chromosomes one with n-1, reciprocal products. Fertilization with normal haploid gamete produces trisomic and monosomic concepti. Mechanism responsible for Down, Turner, Klinefelter syndromes, majority spontaneous abortions early pregnancy, and age-related increase observed maternal meiosis I arrest prolonged decades increasing missegregation risk significantly.