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Genetics · Process

Meiosis Diagram

The stages of meiosis I and II: how one diploid cell becomes four haploid, genetically different gametes, through crossing over and two divisions.

Meiosis makes eggs and sperm. One round of DNA replication is followed by two divisions, so one diploid cell gives four haploid cells, each with one chromosome of every pair: 23 in humans instead of 46. The cell here has two pairs of homologous chromosomes, one long and one short; of each pair, the chromosome from one parent is in ink and the other in grey, so you can follow each one.

Also called Stages of meiosis, Meiosis I and II or Meiosis 1 and 2.

Meiosis in nine panels. Interphase: a diploid cell whose DNA has been copied. Prophase I: the two homologous chromosomes of each pair lie side by side as bivalents inside the nucleus, with a chiasma where two chromatids of the long pair cross. Metaphase I: the two bivalents line up on the metaphase plate, each homologue held by spindle fibres from one pole. Anaphase I: the homologues are pulled to opposite poles, each still two chromatids. Telophase I and cytokinesis: two haploid cells, each with one long and one short chromosome. Metaphase II: in each cell the chromosomes line up singly. Anaphase II: the sister chromatids separate. Telophase II and cytokinesis: four nuclei form. Finally four haploid gametes, each with a different combination of chromosomes.1 InterphaseDNA copied: diploid, two pairs here2 Prophase IHomologues pair and cross over3 Metaphase IBivalents line up on the plate4 Anaphase IHomologues separate, sisters stay5 Telophase I and cytokinesisTwo haploid cells6 Metaphase IIChromosomes line up singly7 Anaphase IISister chromatids separate8 Telophase II and cytokinesisFour nuclei form9 Four haploid gametesAll four differ; n = 23 in humans
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Step 1 of 10

Meiosis at a glance

Meiosis makes gametes. After a single round of DNA replication the cell divides twice, so one diploid cell becomes four haploid cells, each with one chromosome of every pair: 23 in humans instead of 46. On the way, crossing over and the random sorting of the pairs make every gamete genetically different. The cell here has two pairs of homologous chromosomes, one long and one short.

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Step 1 of 10: Meiosis at a glance

Download the diagramChecked against its sources on 5 November 2026.

Step by step

The steps of the Meiosis

  1. 01Meiosis at a glance

    Meiosis makes gametes. After a single round of DNA replication the cell divides twice, so one diploid cell becomes four haploid cells, each with one chromosome of every pair: 23 in humans instead of 46. On the way, crossing over and the random sorting of the pairs make every gamete genetically different. The cell here has two pairs of homologous chromosomes, one long and one short.

  2. 02Interphase: the DNA is copied

    The cell is diploid: it has two of every chromosome, one from each parent, drawn here in ink and in grey. In S phase every chromosome is copied, so each enters meiosis as two identical sister chromatids held together by cohesin. This is the only replication: both divisions share out these copies, and it is that which halves the number.

  3. 03Prophase I: pairing and crossing over

    The longest stage, with sub-stages of its own (leptotene, zygotene, pachytene, diplotene and diakinesis). Each chromosome pairs with its homologue along its whole length, held by a protein scaffold, the synaptonemal complex: the pair is a bivalent, or tetrad of four chromatids. In pachytene two non-sister chromatids break and rejoin, swapping segments; from diplotene this crossing over shows as a chiasma. Almost every pair gets at least one, usually only a few.

  4. 04Metaphase I: bivalents on the plate

    Bivalents, not single chromosomes, line up on the metaphase plate, each held together by its chiasmata. The two sister kinetochores of one homologue attach to fibres from the same pole, and the other homologue faces the opposite pole. Which way round each pair lies is random and independent of the other pairs: Mendel's independent assortment, the second source of new combinations.

  5. 05Anaphase I: the homologues separate

    Cohesin along the chromosome arms is cut, the chiasmata come apart and the homologues are pulled to opposite poles. The sister chromatids of each stay joined, because the cohesin at their centromeres is protected by the protein shugoshin. This is the reductional division: each pole now has one chromosome of every pair, so the number is halved, and here the long chromosome in ink travels with the short one in grey.

  6. 06Telophase I and cytokinesis: two haploid cells

    The cell divides into two haploid cells. Each has one homologue of every pair, still as two chromatids, and the two cells differ: on the left the long chromosome came from one parent and the short one from the other. There is no S phase before the second division; without that omission the chromosome number could not be halved.

  7. 07Metaphase II: like a mitosis

    Meiosis II runs like a mitosis in each of the two cells. The chromosomes line up singly on a new metaphase plate, and now the two sister kinetochores of each attach to opposite poles, exactly as they do in mitosis.

  8. 08Anaphase II and telophase II: the sisters separate

    The cohesin that was left at the centromeres is cut, and the sister chromatids separate and move to opposite poles: the equational division, which leaves the number of chromosomes as it was. A nuclear envelope forms round each of the four sets, and cytokinesis divides each cell in two.

  9. 09Four different gametes

    Four haploid gametes, with 23 chromosomes each in humans. No two are the same: crossing over has made recombinant chromosomes, part ink and part grey, and independent assortment has dealt the homologues of the two pairs in different combinations. In women only one of the four becomes the egg; the others are polar bodies. At fertilisation an egg's 23 chromosomes join a sperm's 23, and the new cell has 46.

  10. 10Compared with mitosis, and when it goes wrong

    Mitosis gives two identical diploid cells, meiosis four different haploid ones. Three things set meiosis I apart: homologues pair and cross over, sister kinetochores attach to the same pole, and cohesin is removed in two steps, arms first and centromeres later. When chromosomes fail to separate (nondisjunction) a gamete gets the wrong number: about 20% of human eggs do, far more than sperm, and an extra chromosome 21, usually from the egg, causes Down syndrome.

Parts

What each part of the meiosis does

Interphase
Before meiosis the diploid cell copies its DNA in S phase, so every chromosome enters meiosis as two identical sister chromatids. There is no further replication between the two divisions.
Prophase I
The longest stage. Homologous chromosomes pair along their length as bivalents, and non-sister chromatids exchange segments by crossing over, seen as chiasmata.
Metaphase I
The bivalents line up on the metaphase plate, each homologue facing one pole. Which way round a pair lies is random and independent of the other pairs.
Anaphase I
The homologues of each pair are pulled to opposite poles, while the sister chromatids stay together: the reductional division, which halves the chromosome number.
Telophase I and cytokinesis
The cell divides into two haploid cells. Each has one chromosome of every pair, still as two chromatids, and goes straight on to meiosis II without copying its DNA.
Metaphase II
In each cell the chromosomes line up singly on a new metaphase plate, with the sister kinetochores now facing opposite poles, as in mitosis.
Anaphase II
The cohesin still holding the centromeres is cut and the sister chromatids separate to opposite poles: the equational division, which leaves the chromosome number unchanged.
Telophase II and cytokinesis
A nuclear envelope forms round each of the four sets of chromosomes, and each of the two cells divides in two.
Haploid gametes
The four cells that result, each with one chromosome of every pair, 23 in humans, and each with a different combination. In men all four become sperm; in women only one becomes the egg and the others are polar bodies. An egg and a sperm fuse at fertilisation to restore the diploid 46.
Homologous chromosomes
The two chromosomes of a pair, one from each parent, carrying the same genes in the same order, though not always the same alleles. One is drawn in ink and the other in grey.
Sister chromatids
The two identical copies of one chromosome made in S phase, joined by cohesin. They stay together through meiosis I and separate only in anaphase II.
Chiasma (crossing over)
The cross-shaped point where two non-sister chromatids of a pair have broken and rejoined, swapping segments. Chiasmata also hold the homologues together until anaphase I.
Bivalent (tetrad)
A pair of homologous chromosomes paired in prophase I, four chromatids in all, held first by the synaptonemal complex and then by its chiasmata. Almost every one has at least one crossover.
Spindle fibres
Microtubules from the two poles that attach to the kinetochores and pull chromosomes apart: whole homologues in meiosis I, sister chromatids in meiosis II.
Centrosome
The organiser of the spindle's microtubules at each pole. Oocytes are an exception: their spindle assembles round the chromosomes without centrosomes.
Metaphase plate
The plane midway between the poles where the bivalents line up in metaphase I and the single chromosomes in metaphase II. It is a position, not a structure.
Nuclear envelope
The double membrane round the nucleus. It breaks up before each division, so the spindle can reach the chromosomes, and re-forms round each new set.
Centromere
The constricted region where the sister chromatids are held together and where the kinetochores form. In meiosis I both sister kinetochores attach to the same pole.
Nucleolus
The part of the nucleus that makes ribosomes. It fades as the chromosomes condense in prophase I.
The cell
The diploid cell dividing here, then the two haploid cells of meiosis II. The nine panels are not to the same scale.

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