Final answer:
Nondisjunction is more likely to occur during meiosis, specifically during meiosis I or II, resulting in gametes with an abnormal chromosome number.
Step-by-step explanation:
Nondisjunction, the failure of chromosomes to separate properly, is more likely to occur during meiosis, specifically during meiosis I or II. During meiosis, the eggs go through the process of cell division to produce gametes. When homologous chromosomes fail to separate during meiosis I, it results in gametes with an abnormal chromosome number. Similarly, if sister chromatids fail to separate during meiosis II, it can also lead to an abnormal chromosome number in the gametes.