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Mitosis vs meiosis: what's the difference?
Two ways cells divide. One copies the cell, the other makes the cells for reproduction.
Mitosis usually produces two genetically identical daughter cells after the cytoplasm divides. Meiosis halves the chromosome number and generates variation. In animals it is part of making gametes, but it does not always produce four functional gametes.
Covers GCSE, AP and A-level. Exam boards differ slightly, so check your course specification.
Side by side
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Making gametes (sperm and egg cells) |
| Number of divisions | One | Two |
| Cells produced | Usually 2 after cytokinesis | Usually 4 haploid products; egg formation gives one large egg and small polar bodies |
| Chromosome number | Same as the parent cell; diploid stays diploid, haploid stays haploid | Half the diploid parent cell (haploid, n) |
| Genetic makeup | Identical to the parent | Different from each other and the parent |
| Homologous chromosomes pair up? | No | Yes |
| Crossing over? | No | Yes, in prophase I |
| Where in humans | Most body cells | Testes and ovaries |
The stages of mitosis
Before mitosis starts, the cell copies its DNA, so each chromosome has two identical sister chromatids. Remember PMAT.
- 01
Prophase
Chromosomes condense and become visible. The nuclear envelope breaks down and spindle fibres form.
- 02
Metaphase
Chromosomes line up along the middle of the cell (the equator), attached to spindle fibres.
- 03
Anaphase
Sister chromatids are pulled apart to opposite ends of the cell.
- 04
Telophase
Nuclear envelopes re-form around each set of chromosomes. Cytokinesis then splits the cytoplasm into two cells.
Two daughter cells with the parent cell's chromosome number
What's different in meiosis
Meiosis has two divisions after one round of DNA copying.
- Meiosis I separates homologous pairs of chromosomes. This is the stage that halves the chromosome number.
- Meiosis II separates sister chromatids, much like mitosis.
Meiosis creates variation in two ways. In crossing over (prophase I), homologous chromosomes swap sections of DNA. In independent assortment (metaphase I), each pair lines up randomly, so chromosomes are shuffled into gametes in different combinations. Random fertilisation adds even more variation.
Typical human body cells have 46 chromosomes (23 pairs) and gametes have 23. Fertilisation restores 46. Sperm formation produces four haploid cells that develop into sperm. Egg formation divides the cytoplasm unequally, giving one large egg and small polar bodies, not four eggs.
Key terms
- Diploid (2n)
- Having two sets of chromosomes, one from each parent. Human body cells have 46.
- Haploid (n)
- Having one set of chromosomes. Human gametes have 23.
- Homologous chromosomes
- A matching pair of chromosomes, one from each parent, carrying the same genes.
- Sister chromatids
- The two identical copies of a chromosome, made by DNA replication and joined together.
- Gamete
- A sex cell: sperm or egg.
- Crossing over
- Homologous chromosomes swapping sections of DNA in prophase I.
Common mistakes
Mitosis doesn't halve the chromosome number. Daughter cells have the same number as the parent.
DNA is copied once, not twice. It's copied before mitosis, and once before meiosis, but not again before meiosis II.
Meiosis I and II do different things. Meiosis I separates homologous chromosomes. Meiosis II separates sister chromatids.
Chromosome vs chromatid. After copying, one chromosome has two sister chromatids. They become separate chromosomes when pulled apart.
A worked example
This is the kind of answer SnapBio gives you when you snap a question: the answer first, then the steps.
A human cell has 46 chromosomes. How many chromosomes are in each cell after meiosis?
How to get there
- 1
Meiosis makes gametes, which have half the chromosome number.
- 2
Half of 46 is 23, one chromosome from each homologous pair.
- 3
Fertilisation then combines two gametes and restores the full 46.
Check yourself
In the standard meiosis model with equal cytokinesis, how many haploid cells are produced?
Two meiotic divisions with equal cytokinesis produce four haploid cells. Egg formation is different: most cytoplasm stays in one egg, with small polar bodies.
Which process produces two genetically identical cells?
Mitosis produces two daughter cells that are genetically identical to the parent.
When does crossing over happen?
Homologous chromosomes pair up and swap sections in prophase I of meiosis.
FAQ
Why is meiosis important?
It halves the chromosome number so that fertilisation restores the full number, and it creates genetic variation through crossing over and independent assortment.
How many cells does mitosis produce?
Two daughter cells, each genetically identical to the parent cell.
What is the difference between a chromosome and a chromatid?
After DNA replication, each chromosome is made of two identical sister chromatids joined together. Once the chromatids are pulled apart, each is counted as its own chromosome.
Does DNA replicate before meiosis?
Yes, once, before meiosis I. It does not replicate again before meiosis II. See DNA replication explained.
Sources and further reading
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