During which stage of meiosis does nondisjunction typically occur?

Nondisjunction typically occurs during the separation of homologous chromosomes or sister chromatids, which can happen in different stages of meiosis. The most common stage for nondisjunction to occur is during Metaphase I or Anaphase I, where homologous chromosomes fail to separate properly.

During Metaphase I, chromosomes align at the cell's equatorial plane, and if the spindle fibers do not attach correctly or if there is a failure in the checkpoint mechanisms, this can lead to nondisjunction. In Anaphase I, if the homologous chromosomes do not separate as they should, both chromosomes might be pulled to one pole, while the other pole receives none.

While Prophase I is where homologous chromosomes pair up and can undergo recombination, the actual separation issues that lead to nondisjunction occur later in Metaphase or Anaphase. Thus, while nondisjunction can occur in different stages of meiosis, it is primarily during the stages that involve the actual movement and separation of chromosomes that this process is critical.

Overall, the key understanding here is that nondisjunction is a failure in the proper segregation of chromosomes during meiosis, typically occurring in or around the Metaphase or Anaphase