What is the difference between mitosis and meiosis, and why does each matter?
Mitosis as cell division producing two genetically identical cells for growth and repair, meiosis as division producing four genetically different gametes with half the chromosome number, and why meiosis creates variation.
A focused CCEA GCSE Biology answer on cell division, covering mitosis producing identical cells for growth and repair, meiosis producing genetically different gametes with half the chromosome number, and why meiosis creates variation.
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What this dot point is asking
CCEA wants you to describe mitosis as the division that makes two genetically identical cells for growth and repair, describe meiosis as the division that makes four genetically different gametes with half the chromosome number, and explain why meiosis creates variation.
Mitosis
Before mitosis the DNA is copied exactly, so each new cell receives a complete, identical set of chromosomes.
Meiosis
Why the chromosome number is halved
If gametes had the full 46 chromosomes, joining two at fertilisation would give 92, and the number would keep doubling each generation. Halving it in meiosis means fertilisation restores the normal 46, keeping it constant.
Examples in context
- Example 1. Healing a cut
- When you cut your skin, the body repairs it by making new cells through mitosis. The cells around the wound copy their DNA and divide to produce genetically identical cells, replacing those that were lost. Because the cells are identical, the new skin matches the old. This everyday example shows mitosis at work in growth and repair, where identical copies are exactly what is needed.
- Example 2. Why sexual reproduction creates variety
- A field of clover grown from cuttings (asexual reproduction by mitosis) is genetically identical, so if a disease can kill one plant it can kill them all. Clover grown from seed (sexual reproduction involving meiosis) is varied, so some plants may resist the disease and survive. This contrast shows the advantage of the variation that meiosis and fertilisation produce, and it links cell division to natural selection.
- Example 3. Where each type of division happens in the body
- Almost all of the cell division in your body is mitosis: it makes new cells as you grow, replaces worn-out cells such as skin and blood cells, and heals wounds, always producing genetically identical copies. Meiosis happens only in the reproductive organs, the testes and ovaries, where it makes the gametes (sperm and eggs). This is why a child grows by mitosis but can only be made by the meiosis that produced the gametes of its parents. Knowing where each type of division occurs, mitosis throughout the body and meiosis only in the sex organs, helps you choose the right division in an exam question and explains why the two have such different products.
Try this
Q1. How many cells does meiosis produce from one parent cell? [1 mark]
- Cue. Four.
Q2. Why must gametes have half the normal chromosome number? [2 marks]
- Cue. So that fertilisation joins two gametes and restores the full number, rather than doubling it each generation.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20204 marksCompare the products of mitosis and meiosis.Show worked answer →
Four marks for paired contrasts about number, chromosomes and genes.
Mitosis produces two daughter cells; meiosis produces four.
Mitosis produces cells with the full chromosome number (diploid, 46 in humans); meiosis produces cells with half the chromosome number (haploid, 23 in humans).
Mitosis produces genetically identical cells; meiosis produces genetically different cells.
Mitosis is used for growth and repair; meiosis makes gametes (sex cells) for reproduction.
Markers reward at least two correct contrasts: two versus four cells, full versus half chromosome number, identical versus different, growth versus gamete formation.
CCEA 20183 marksExplain why meiosis is important in sexual reproduction.Show worked answer →
Three marks for the halved number and the variation.
Meiosis halves the chromosome number, so each gamete has 23 chromosomes (haploid).
This means that when two gametes join at fertilisation, the normal number (46) is restored, not doubled.
Meiosis also produces genetically different gametes, which leads to variation in the offspring.
Markers reward halving the chromosome number, restoring the full number at fertilisation, and producing variation.
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Sources & how we know this
- CCEA GCSE Biology specification — CCEA (2017)