In which stage of cell division does cell division begin?

The stage at which cell division begins is prophase. During prophase, several critical events occur that set the stage for cell division. The chromatin condenses into visible chromosomes, and the nuclear envelope starts to break down. Spindle fibers also begin to form and attach to the chromosomes at their centromeres, preparing them for separation. This phase is essential as it establishes the structural organization necessary for the chromosomes to be accurately divided between the two new cells in subsequent stages.

In contrast, the other stages of cell division do not represent the initiation of the process. Anaphase involves the separation of the sister chromatids and their movement to opposite poles, telophase marks the end of nuclear division and the reformation of the nuclear envelope around the separated sets of chromosomes, and metaphase is characterized by the alignment of chromosomes along the cell's equatorial plane, preparing them for separation. Each of these stages follows prophase in the cell division process.