Every time you heal a cut, grow a fingernail, or replace old blood cells, mitosis is quietly doing the work. It's one of the most fundamental processes in biology — and once you see the four stages, it's impossible to unsee.
Mitosis is the process a cell uses to divide into two genetically identical daughter cells. It's how organisms grow from a single fertilised egg into trillions of cells, how wounds close, and how tissues constantly replace worn-out cells. The process is tightly regulated, highly accurate, and happens billions of times a day inside your body right now.
Prophase
Chromosomes condense into visible X-shapes, the nuclear envelope breaks down, and spindle fibers begin to form.
Metaphase
Chromosomes line up single-file along the cell's equator, each attached to spindle fibers from opposite poles.
Anaphase
Sister chromatids are pulled apart and travel to opposite ends of the cell — the "separation" moment.
Telophase
Two new nuclei form around each set of chromosomes, and the cell prepares to split in two.
What Is Mitosis?
CELL DIVISIONMitosis is a type of cell division that produces two daughter cells with the same number of chromosomes as the original parent cell. It's the engine behind growth, tissue repair, and asexual reproduction in many organisms.
Before mitosis begins, the cell goes through interphase — a preparation phase where it grows, copies its DNA, and makes sure everything is ready. Once the DNA is duplicated, mitosis can proceed. Each chromosome now consists of two identical sister chromatids joined at a central point called the centromere. Those chromatids will eventually become the genetic material of the two new cells.
Mitosis is about making more of the same. It creates two cells that are genetically identical to the parent. This is different from meiosis, which produces genetically unique sex cells.
The Four Stages of Mitosis, Step by Step
PROPHASE · METAPHASE · ANAPHASE · TELOPHASEMitosis is traditionally divided into four main stages, though in reality it's a smooth, continuous process. The stages are mainly a useful way to describe what's happening at each phase.
1. Prophase
Prophase is the opening act. Several things happen at once:
- Chromatin (the loose, thread-like form of DNA) condenses into tightly packed, visible chromosomes — usually X-shaped because each is made of two sister chromatids.
- The nuclear envelope, which normally surrounds the nucleus, breaks down.
- The centrosomes (the cell's microtubule-organising centres) move to opposite poles of the cell.
- Spindle fibers begin growing out from the centrosomes toward the centre of the cell.
At the end of prophase, the stage is set: chromosomes are visible, the nuclear barrier is gone, and the spindle machinery is in place.
2. Metaphase
Metaphase is the "middle" phase — literally. The chromosomes line up along the cell's equator, forming what's called the metaphase plate. Each chromosome is attached to spindle fibers coming from opposite poles, one fiber per sister chromatid.
This alignment is crucial: it ensures that when the chromatids are pulled apart, each daughter cell gets exactly one copy of every chromosome. The cell has a checkpoint here (the spindle checkpoint) that pauses division if any chromosome isn't properly attached.
3. Anaphase
Anaphase is the most visually dramatic stage. The spindle fibers shorten, pulling the sister chromatids apart at the centromere. Each chromatid — now an independent chromosome — is dragged toward its respective pole.
By the end of anaphase, the cell has two complete, identical sets of chromosomes, one at each end. The cell also elongates slightly as the poles push apart.
4. Telophase
Telophase is the cleanup and reset phase. Around each set of chromosomes, a new nuclear envelope forms. The chromosomes begin to decondense back into chromatin. The spindle fibers disassemble.
At this point, the cell has two nuclei within a single cytoplasm. The final physical split — cytokinesis — usually happens alongside telophase. In animal cells, a contractile ring pinches the cell into two. In plant cells, a cell plate forms down the middle, eventually becoming a new cell wall.
The order PMAT — Prophase, Metaphase, Anaphase, Telophase — is the standard mnemonic. Some textbooks add a "prometaphase" stage between prophase and metaphase, but the four-stage model is the most widely taught.
Interactive: Watch Mitosis Progress
Use the slider below to move through the stages of mitosis. The diagram updates live, showing chromosomes, spindle fibers, and the nuclear envelope at each step.
Slide through Prophase → Metaphase → Anaphase → Telophase. Watch how the chromosomes move and the cell prepares to divide.
Mitosis vs Meiosis: What's the Difference?
Mitosis and meiosis are both forms of cell division, but they serve very different purposes. Here's a side-by-side comparison.
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Production of gametes (sperm, egg) |
| Number of divisions | One | Two |
| Daughter cells | 2 | 4 |
| Chromosome number | Same as parent (diploid) | Half of parent (haploid) |
| Genetic variation | None — identical copies | Yes — crossing over and independent assortment |
| Where it happens | Almost all body cells | Reproductive organs only |
Why Mitosis Matters
Without mitosis, complex life as we know it wouldn't exist. Here's why it's so important:
- Growth: A single fertilised egg becomes trillions of cells through repeated mitosis.
- Repair: Damaged tissues — skin, muscle, bone — are rebuilt by dividing cells.
- Replacement: Red blood cells, gut lining cells, and skin cells are constantly worn out and replaced.
- Asexual reproduction: Many organisms (like yeast and some plants) reproduce by mitosis alone.
Uncontrolled mitosis is the hallmark of cancer. When the checkpoints that normally regulate cell division fail, cells can divide endlessly, forming tumours. Understanding mitosis is therefore central to cancer research.