Definition · Plain-language
Meiosis
Meiosis is the type of cell division that produces four genetically different sex cells, each with half the usual number of chromosomes.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
Cell division for reproduction
Meiosis is the special cell division that makes gametes — the sex cells, such as sperm and egg in animals or pollen and ovules in plants. Unlike ordinary cell division, which copies cells exactly, meiosis has a different goal: to produce cells with half the genetic material, ready to combine with another gamete. It takes place only in the reproductive organs. From one starting cell, meiosis produces four gametes, and crucially each of the four is genetically unique.
Why it halves the chromosomes
Body cells carry two sets of chromosomes, one from each parent — in humans, 46 in total. If gametes had the full 46, fertilisation would create a cell with 92, doubling the number every generation. Meiosis prevents this by halving the chromosome number: each human gamete carries 23. When a sperm (23) fertilises an egg (23), the new cell has the normal 46 again. This halving, called reduction division, is the central purpose of meiosis and the reason it involves two divisions rather than one.
How it creates variation
Meiosis is a major source of the genetic variation that makes individuals differ. Two processes are responsible. In crossing over, paired chromosomes swap matching sections, mixing the alleles inherited from each parent. In independent assortment, the chromosome pairs line up and separate at random, so each gamete gets a different combination of the parents’ chromosomes. Together these shuffle the genes into countless combinations, which is why siblings (other than identical twins) are never genetically the same.
Key facts
At a glance
- Definition: cell division that makes gametes for sexual reproduction
- Cells made: four, each genetically different
- Chromosomes: halved (e.g. 46 to 23 in humans)
- Divisions: two in a row (meiosis I and II)
- Where: in the reproductive organs only
- Creates: genetic variation via crossing over and independent assortment
Common misconceptions
What people often get wrong
Often heard: Meiosis produces two identical cells, like ordinary cell division.
Actually: That describes mitosis. Meiosis produces four cells, each genetically different from the others and from the parent, and each with half the chromosome number. The difference reflects their different purposes — growth versus reproduction.
Often heard: Meiosis happens in all body cells.
Actually: Meiosis happens only in the reproductive organs, where gametes are made. Ordinary body cells divide by mitosis for growth and repair. A skin or muscle cell never undergoes meiosis.
Often heard: The cells made by meiosis have the full set of chromosomes.
Actually: Gametes carry only half the usual chromosome number. The full set is restored at fertilisation, when two gametes join. If gametes kept the full number, it would double every generation.
Going deeper
