Cell BiologyStep-through12 minLesson 1 of 7

Mitosis

Every cell in your body came from a single fertilized egg through billions of rounds of mitosis. Learn how one cell becomes two — with perfect genetic fidelity — every time.
Chromatin
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Interphase
Cytokinesis

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Phase 1 of 6

Interphase

G₂ — Preparation

The cell has already duplicated its DNA and is growing in preparation for division. Chromosomes exist as loosely coiled chromatin — not yet condensed into visible X shapes.

  • DNA was fully replicated during S phase
  • Cell grows and synthesizes division proteins
  • Centrosomes have been duplicated
Predict before you continue

The DNA was copied during S phase. What happens to it first when mitosis begins?

Why mitosis matters

Mitosis is the engine of growth, maintenance, and repair in multicellular life. Understanding it is foundational to understanding cancer, wound healing, and development.

  • 46 → 46

    Mitosis is a copying process, not a halving one. Each daughter cell receives a complete copy of all 46 chromosomes — identical to the parent cell.

  • 1–2 Hours

    A full mitotic cycle takes about 1–2 hours in human cells. Interphase can last 18–20 hours — the actual division is the quick part.

  • Not Meiosis

    Mitosis produces 2 identical diploid cells for growth and repair. Meiosis produces 4 genetically diverse haploid cells for sexual reproduction.

Real world

What happens when mitosis goes wrong?

Errors at the spindle assembly checkpoint can let chromosomes mis-segregate, giving daughter cells the wrong number — aneuploidy. When these errors affect genes that control the cell cycle, the result can be uncontrolled division: cancer. Many chemotherapy drugs disrupt spindle formation, freezing cells at metaphase so they self-destruct.

Quick recap

  1. 1

    Interphase (G₂) — Cell grows; DNA already duplicated — ready to divide.

  2. 2

    Prophase — Chromosomes condense; nuclear envelope breaks down; spindle forms.

  3. 3

    Metaphase — Chromosomes line up at equator; spindle checkpoint fires.

  4. 4

    Anaphase — Sister chromatids pulled to opposite poles; cell elongates.

  5. 5

    Telophase — Nuclear envelopes reform; chromosomes decondense; furrow starts.

  6. 6

    Cytokinesis — Cleavage furrow pinches cell in two → 2 identical daughter cells.