AP BIOLOGY

Detailed explanation-1: -In nondisjunction, the separation fails to occur causing both sister chromatids or homologous chromosomes to be pulled to one pole of the cell.

Detailed explanation-2: -Nondisjunction occurs when homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis. An individual with the appropriate number of chromosomes for their species is called euploid; in humans, euploidy corresponds to 22 pairs of autosomes and one pair of sex chromosomes.

Detailed explanation-3: -Nondisjunction is caused due to inactivation of topoisomerase II, separase or condensin. During anaphase, the cohesin which binds the sister chromatids together is broken by separase. Catenation is removed by condensin and topoisomerase II. Segregation of chromosomes is regulated by spindle assembly checkpoint or SAC.

Detailed explanation-4: -The difference between non-disjunction in meiosis I and meiosis II is that during meiosis I when genetic material is divided, non-disjunction results in abnormal homologous chromosomes. In meiosis II non-disjunction results in abnormal sister chromatids.