What is the primary event that takes place during the M phase of the cell cycle?

The primary event that occurs during the M phase of the cell cycle is nuclear division, also known as mitosis. This phase is where the replicated chromosomes are separated into two new nuclei, ensuring that each daughter cell receives an identical set of chromosomes. Mitosis involves several key stages, including prophase, metaphase, anaphase, and telophase, all of which are critical for the proper distribution of genetic material.

While cytokinesis is often associated with the M phase, as it follows nuclear division and completes the cell division process by dividing the cytoplasm, the actual division of the nucleus is the hallmark of the M phase itself. DNA replication occurs during the S phase, prior to M phase, ensuring that the cell has two complete sets of DNA. Chromosome condensation is also part of the process but is specifically a precursor to anaphase during mitosis rather than the main event. Thus, nuclear division is the most accurate representation of the primary event during the M phase.