Library · Cellular process
Meiosis
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Meiosis is the special type of division that makes sperm and eggs. These cells end up with a haploid set of chromosomes, that is, half the usual number. Think of a deck made of pairs of cards: that is the diploid set. The sperm brings one card from each pair, the egg brings the other card from each pair, and when they unite at fertilization, all the pairs are complete again.
To get there, the cell goes through two divisions in a row. In the first, the chromosomes come together in pairs; the two chromosomes in each pair are called homologous chromosomes. While they are together, they can randomly swap segments, which is called crossing over, and then the members of each pair move to opposite sides. In the second division, the sister chromatids, the two copies of each chromosome, separate.
The result is that each daughter cell shares half its genetic makeup with the cell it came from, yet it is different from that cell and from the other daughter cells.
In brief
Meiosis is the division that produces sperm and eggs with a haploid set, half the chromosomes, so that fertilization restores the diploid set.
Egg and sperm each bring one card from every pair; when they unite, the pairs are complete again.
It happens in two divisions: in the first, homologous chromosomes pair up, can randomly exchange segments (crossing over), and separate; in the second, sister chromatids separate.
Each daughter cell shares half its genetic makeup with its parent cell but differs from it and from the others.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingGenetics, Meiosis, StatPearlsPublished
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