Nondisjunction occurs during which phase of cell division?

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. This process can lead to gametes with an abnormal number of chromosomes, which is a critical aspect of genetic variability and can result in conditions such as Down syndrome or other chromosome abnormalities.

In meiosis, particularly during anaphase I or anaphase II, nondisjunction can occur. During anaphase I, homologous chromosomes fail to separate, while during anaphase II, sister chromatids do not separate. This contrasts with mitosis, where the processes are more regulated, and such errors are less common. The other options, interphase and replication, refer to the preparatory stages of the cell cycle and do not involve the actual separation of chromosomes. Therefore, nondisjunction is specifically associated with meiosis, making it the correct choice in this context.