Answer/Explanation:
Nondisjunction is when homologous chromosomes or sister chromatids fail to properly separate during meiosis. This means daughter cells have an incorrect set of chromosomes.
Nondisjunction occurs during meiosis I or II, with different results in each. The outcomes at either meiosis i or meiosis ii are shown in the attached picture (nondisjunction at meiosis ii on the left (blue arrow) and nondisjunction at meiosis i on the right (dark green arrow)
Nondisjunction during meiosis i
Nondisjunction during meiosis i occurs when homologous chromosomes fail to properly separate. This results in two gametes without that chromosome, and two gametes with two copies of that chromosome. This is wrong, as each gamete should have one copy.
Nondisjunction during meiosis ii
If the sister chromatids fail to separate during meiosis II (the homologous chromosomes have already successfully separated), then there will be two normal gametes that have one copy of the chromosome (correct), one gamete will not have that chromosome, and one gamete with two copies of the chromosome.
