5.2.3—Main stages of mitosis

Mitosis is the ordered division of one nucleus into two genetically matching nuclei. The four named stages are prophase, metaphase, anaphase and telophase (PMAT); interphase prepares the cell but is not one of these four stages.

1. Prophase — condense and prepare: Chromosomes condense and become distinct; each still has two sister chromatids joined at a centromere. The nuclear envelope breaks down and the spindle forms. The nucleus is being prepared for chromosome movement; the cytoplasm has not yet divided.
2. Metaphase — align and connect: Replicated chromosomes arrange at the cell equator. Spindle fibres attach at the centromere regions and connect the sister chromatids to opposite poles. This alignment provides the starting point for equal separation.
3. Anaphase — separate and move: Centromeres divide, so sister chromatids become individual chromosomes. Spindle fibres shorten and pull the separated chromosomes to opposite poles, forming two genetic-material groups.
4. Telophase — re-form nuclei: Chromosomes reach opposite poles and begin to decondense. A nuclear envelope reforms around each chromosome group and the spindle is dismantled. Cytokinesis then divides the cytoplasm, completing separation into two cells.

The PMAT sequence links chromosome state to movement: condensation makes chromosomes movable, spindle attachment and equatorial alignment establish opposite-pole routes, centromere division permits sister chromatids to separate, and arrival at the poles allows two nuclei to reform. Cytokinesis follows nuclear division to partition the cytoplasm, rather than being an additional PMAT stage.

Do not include interphase in PMAT: DNA replication occurs before mitosis. Card 4566 explains the chromosome-separation logic in more detail, and card 4567 covers coordinated nuclear-envelope, spindle and cell-boundary behaviour; this card is the ordered stage map. A micrograph or slide is interpreted separately in card 4569.