MeiosisCambridge IGCSE Biology: Revision notes
Section 1
What Is Meiosis?
Meiosis is a reduction division: a type of nuclear division in which the chromosome number is halved from diploid to haploid, producing cells that are genetically different from each other and from the parent cell.
Recall: a diploid nucleus contains two sets of chromosomes; a haploid nucleus contains a single set.
Section 2
Where Does Meiosis Happen and Why?
Meiosis is involved in the production of gametes (sex cells, e.g. sperm and egg cells). In a diploid cell, there is a pair of each type of chromosome; in a human diploid cell there are 23 pairs (46 chromosomes in total).
Meiosis divides this diploid number down to a single haploid set of 23 chromosomes in each gamete. When two gametes fuse at fertilisation, the diploid number is restored in the zygote.
If a question gives you the diploid number of a species and asks for the number of chromosomes in a gamete, simply halve it.
Section 3
How Does Meiosis Differ from Mitosis?
| Feature | Mitosis | Meiosis |
|---|---|---|
| Chromosome number in daughter cells | Same as parent (diploid → diploid) | Halved (diploid → haploid) |
| Genetic identity of daughter cells | Genetically identical | Genetically different |
| Main purpose | Growth, repair, replacement, asexual reproduction | Production of gametes for sexual reproduction |
A common error is saying meiosis 'produces identical cells' — meiosis produces genetically different haploid cells; only mitosis produces identical cells.
Must Know
- Meiosis is a reduction division: diploid → haploid
- Meiosis produces genetically different cells (unlike mitosis, which produces identical cells)
- Meiosis is involved in the production of gametes
- A human diploid cell has 23 pairs of chromosomes (46 total); a human gamete has 23 (haploid)
- Fertilisation restores the diploid number when two haploid gametes fuse
That's the notes covered.
Carry on to the next subtopic.