During which phase of cell division does the number of chromosomes halve?

The number of chromosomes is halved during the first meiotic division, specifically in Meiosis I. This division consists of several phases, with Prophase I being the initial phase where homologous chromosomes pair up and exchange genetic material through a process called crossing over.

However, it is during the subsequent phases, notably Anaphase I, that the homologous chromosomes are pulled apart to opposite poles of the cell, resulting in two new daughter cells with half the number of chromosomes. By the end of Telophase I, the cell division completes, and the two resultant cells have undergone reduction in chromosome number, but the key processes that lead to the halving occur in Prophase I as it sets up the necessary conditions for chromosome separation.

The confusion may arise because it may seem like Telophase I is the appropriate choice since it marks the conclusion of the first meiotic division. However, the actual halving of the chromosomes directly relates back to the pairing and separation processes that commence in Prophase I.