Mitosis vs meiosis: the differences explained
TutorAura guide · Updated
Mitosis makes two genetically identical cells for growth and repair. Meiosis makes four genetically different gametes (sex cells) with half the number of chromosomes. In humans, body cells have 46 chromosomes (23 pairs) and gametes have 23.
Key takeaways
- Mitosis: 2 identical cells with the full chromosome number.
- Meiosis: 4 different gametes with half the chromosome number.
- Mitosis is for growth, repair and asexual reproduction.
- Meiosis creates variation; fertilisation restores the full number.
Side by side
| Mitosis | Meiosis | |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Making gametes for sexual reproduction |
| Divisions | One | Two |
| Cells produced | 2 | 4 |
| Chromosome number | Same as the parent cell (46 in humans) | Half (23 in humans) |
| Genetically | Identical to the parent and each other | Different from each other |
| Where (humans) | Body cells all over the body | Testes and ovaries |
The cell cycle and mitosis
Before a cell divides by mitosis, it grows, copies its organelles (such as mitochondria and ribosomes) and copies its DNA, so each chromosome has two identical copies. In mitosis, one copy of each chromosome is pulled to each end of the cell. The cytoplasm and cell membrane then divide, making two identical cells.
Meiosis and variation
In meiosis, the cell divides twice. Each gamete gets one chromosome from each pair, and which one ends up in which gamete is random. That's why siblings (other than identical twins) differ. At fertilisation, a sperm (23) and egg (23) join to make a zygote with 46 chromosomes, which then grows by mitosis.
Why it matters
- Mitosis lets organisms grow, replace damaged cells and, in some cases, reproduce asexually (making clones).
- Meiosis and fertilisation create genetic variation, which helps populations survive changes in their environment through natural selection.
Inheritance of alleles in gametes is shown with Punnett squares.
Memory tips
- Mitosis makes identical cells.
- Meiosis makes eggs (and sperm).
- "Two" for mitosis (cells), "four" for meiosis (cells).
Common mistakes
- Saying meiosis makes identical cells.
- Saying gametes have 46 chromosomes.
- Confusing chromosomes with genes: a chromosome carries many genes.
Asexual and sexual reproduction
Asexual reproduction uses mitosis and needs only one parent. The offspring are genetically identical clones, as in bacteria splitting, strawberry runners and potato tubers. It's fast, but there's no variation.
Sexual reproduction uses meiosis to make gametes, which then join at fertilisation. Offspring get a mix of genes from two parents, so there is variation, which helps a species survive changes in its environment.
When cell division goes wrong
Normally, cells divide only when needed. Changes in a cell can lead to uncontrolled cell division, forming a tumour. Benign tumours stay in one place; malignant tumours are cancers, which can invade nearby tissue and spread to other parts of the body.
Practice questions
- How many cells does one cell make in meiosis?
- A cell with 46 chromosomes divides by mitosis. How many chromosomes are in each new cell?
- Which type of division is used to repair a cut in the skin?
Answers: 4; 46; mitosis.
Frequently asked questions
What happens before a cell divides by mitosis?
The cell grows, makes more organelles such as mitochondria and ribosomes, and copies its DNA so each chromosome has two identical copies.
What is a zygote?
The cell formed when a sperm and an egg fuse at fertilisation. It has the full number of chromosomes and divides by mitosis to form an embryo.
Where does meiosis happen in plants?
In the reproductive organs: the anthers, where pollen is made, and the ovaries, where ovules are made.
What is the main difference between mitosis and meiosis?
Mitosis makes two identical cells with the full number of chromosomes; meiosis makes four genetically different gametes with half the number.
How many chromosomes are in a human gamete?
23, half the 46 in a body cell.
Why is meiosis important?
It halves the chromosome number so fertilisation restores the full number, and it creates genetic variation.
Sources
- GCSE Biology (8461) specification: subject content. AQA.
- Cambridge IGCSE Biology 0610 syllabus for 2026, 2027 and 2028. Cambridge International.
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