Mitosis and meiosis — Cambridge IGCSE Biology
Mitosis gives genetically identical cells for growth and repair; stem cells; meiosis halves the chromosome number to make gametes.
Revision notes
3 short notes, in the order of the specification. Each one in short:
Mitosis is nuclear division giving rise to genetically identical cells. Before mitosis the chromosomes are exactly replicated, and during mitosis the copies separate, one into each new nucleus, so the chromosome number is maintained. Mitosis is used for growth, repair of damaged tissues, replacement of cells such as skin cells, and asexual reproduction.
A stem cell is an unspecialised cell that divides by mitosis to produce daughter cells that can become specialised for specific functions, such as red blood cells or nerve cells. Some daughter cells stay as stem cells, so the supply is not used up. Cells become specialised because only some of their genes are expressed.
Meiosis is a reduction division that halves the chromosome number from diploid to haploid, producing gametes that are genetically different from each other and from the parent cell. It takes place in the testes and ovaries. In humans, gametes with 23 chromosomes are made from cells with 46, so fertilisation restores 46 in the zygote.
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Quick check questions
Supplement Define mitosis.
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Nuclear division giving rise to genetically identical cells.
Supplement State four roles of mitosis.
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Growth, repair of damaged tissues, replacement of cells, asexual reproduction.
Supplement What happens to the chromosomes before mitosis?
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They are copied exactly (replicated).
Supplement What is a stem cell?
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An unspecialised cell that divides by mitosis to produce daughter cells that can become specialised.
Supplement What happens to the chromosome number in meiosis?
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It is halved, from diploid to haploid.
Frequently asked questions
What is the difference between mitosis and meiosis?
Mitosis produces two genetically identical diploid cells, while meiosis produces four genetically different haploid cells. Mitosis is used for growth, repair, cell replacement and asexual reproduction. Meiosis is a reduction division used to make gametes in the testes and ovaries, halving the chromosome number from diploid to haploid.
Why is meiosis important for sexual reproduction?
Meiosis is important because it halves the chromosome number, so gametes are haploid. When a sperm fertilises an egg, the full diploid number is restored in the zygote: 46 chromosomes in humans. If gametes were diploid, the chromosome number would double in every generation. Meiosis also makes gametes genetically different.
Why are stem cells useful?
Stem cells are useful because they are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised, such as red blood cells or nerve cells. Some daughter cells stay as stem cells, so the supply is not used up. They become specialised when only some of their genes are expressed.
What happens to chromosomes during mitosis?
Before mitosis, the chromosomes are exactly replicated, so each chromosome is made of two identical copies. During mitosis, the copies separate and one copy goes into each new nucleus. This maintains the chromosome number, so the two daughter cells have the same number of chromosomes and the same genes as the parent cell.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026