Edexcel IGCSE Biology · Spec 3.28-3.32
Mitosis and Meiosis
The two types of cell division — mitosis and meiosis — and where each is used in the body.
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Mitosis and Meiosis
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Explained
Mitosis and meiosis: two divisions, two very different products
Mitosis makes two cells that are genetically identical to the parent cell and to each other, and they are diploid. Meiosis makes four cells that are all genetically different, and they are haploid. Two identical against four different is the comparison every question in this topic rests on.
Diploid and haploid
A diploid cell has the full set of chromosomes, which in humans is 46. A haploid cell has half the set, which is 23. Gametes are haploid, which is the reason the number works: 23 from a sperm and 23 from an egg give a zygote with 46, and the species keeps the same chromosome number generation after generation.
If gametes were diploid, the number would double every generation. That is the simplest way to explain why meiosis has to halve it.
Where each one is used
Mitosis is used for growth, for repairing damaged tissue, and for asexual reproduction. Every new cell must be a copy, which is exactly what mitosis produces.
Meiosis is used only to make gametes, in the testes and the ovaries. Producing variation is the point of it, not a side effect.
Where the variation comes from
Meiosis produces four cells that differ from one another, and fertilisation then combines two of these at random. Variation therefore arises twice over: once when the gametes are made, and again in which gamete happens to fuse with which.
Asexual reproduction uses mitosis alone, so the offspring are genetically identical to the parent. That is why questions comparing the two forms of reproduction almost always come back to variation.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Biology list the common correct answers on sexual reproduction as the production of genetic variation, the roles of mitosis and meiosis, and the need for fusion of haploid gametes. Those three ideas together make a complete answer.
Reports also show this area examined through genetic diagrams, where full marks require the parent genotypes, the gametes they can produce, the offspring genotypes and the ratio of phenotypes. Missing out the gametes row is a common way to score three out of four rather than full marks.
A comparison worth writing out
If you are asked to compare the two, answer in matched pairs: number of cells produced, whether they are identical or different, diploid or haploid, and where in the body each happens. Four pairs, four contrasts, and nothing left to chance.
Spec 3.28-3.32
What you need to know
- Describe what mitosis produces and where it is used
- Describe what meiosis produces and where it is used
- Recall the diploid and haploid chromosome numbers
Active recall
Quick check
Answer each question before opening the answer.
Compare the products of mitosis and meiosis.
Mitosis makes two genetically identical diploid cells (for growth/repair); meiosis makes four genetically different haploid cells (gametes).
Which type of division produces genetic variation?
Meiosis.
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