CorpusHuman Anatomy

Mitosis and Cytokinesis

From a G2 cell to two genetically identical daughter cells

The stages of M phase, left to right, in an idealised diploid cell with two pairs of homologous chromosomes (maternal pink, paternal blue). Each chromosome was replicated in S phase and so consists of two identical sister chromatids joined at the centromere, where the kinetochores (white dots) attach to spindle microtubules. Two centrosomes, duplicated during interphase, organise the spindle poles.

Animations show the centrosomes separating in prophase, chromosomes being jostled as microtubules capture them in prometaphase, the small oscillations of aligned chromosomes at the metaphase plate, the synchronous poleward movement of sister chromatids as kinetochore microtubules shorten in anaphase, and the actin–myosin ring constricting the cleavage furrow in cytokinesis. Mitosis takes about an hour in a typical human cell.

Step-by-step

  1. Interphase (G2)

    Before mitosis the DNA has been replicated (S phase) and the centrosome duplicated. Chromatin is diffuse, the nucleolus is visible and the nuclear envelope intact. Rising cyclin B–CDK1 activity at the G2/M checkpoint launches mitosis.

  2. Prophase

    Chromosomes condense into visible pairs of sister chromatids; the nucleolus disappears; centrosomes separate and nucleate the spindle.

  3. Prometaphase

    The nuclear envelope breaks down; spindle microtubules capture chromosomes at their kinetochores and start moving them toward the equator.

  4. Metaphase

    Chromosomes line up at the metaphase plate with sister kinetochores facing opposite poles. The spindle-assembly checkpoint waits until all are attached.

  5. Anaphase

    Separase cleaves cohesin; sister chromatids separate and move to opposite poles (anaphase A) while the spindle elongates (anaphase B).

  6. Telophase and cytokinesis

    Nuclear envelopes and nucleoli re-form around two identical chromosome sets, chromosomes decondense, and the actin–myosin contractile ring pinches the cell into two daughter cells.

Labelled parts

  • Interphase (late G2)
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase and cytokinesis