meiosis

American  

[mahy-oh-sis] / maɪˈoʊ sɪs /

noun

1. Cell Biology. part of the process of gamete formation, consisting of chromosome conjugation and two cell divisions, in the course of which the diploid chromosome number becomes reduced to the haploid.

2. Rhetoric.

   1. belittlement.

   2. expressive understatement, especially litotes.

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meiosis British  

/ maɪˈɒtɪk, maɪˈəʊsɪs /

noun

1. a type of cell division in which a nucleus divides into four daughter nuclei, each containing half the chromosome number of the parent nucleus: occurs in all sexually reproducing organisms in which haploid gametes or spores are produced Compare mitosis See also prophase

2. rhetoric another word for litotes

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meiosis Scientific  

/ mī-ō′sĭs /

1. The process in cell division in sexually reproducing organisms that reduces the number of chromosomes from diploid to haploid (half the original number). Meiosis involves two consecutive divisions of the nucleus and leads to the production of reproductive cells (gametes) in animals and to the formation of spores in plants, fungi, and most algae (the haploid spores grow into organisms that produce gametes by mitosis). Meiosis begins when the chromosomes, which have already duplicated, condense along the center of the nucleus, and pairs of homologous chromosomes undergo crossing over, whereby some of their genetic material is exchanged. The pairs of chromosomes then separate and move to opposite ends of the cell, and the cell itself divides into two cells. In the second stage, each of these two cells also divides into two cells. Meiosis thus produces four cells, each of which contain half the number of chromosomes as the original cell. Some or all of the four cells may become functional gametes or spores.

2. Compare mitosis

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meiosis Cultural  

1. Division of cells in which four “daughter” cells are produced from one “parent” cell, each with half the genes of the parent. Meiosis is a key process in sexual reproduction. In the ovaries and testes, meiosis produces a great variety of sex cells (sperm and ova), because the genes of the parent cell can be split in many different ways. The sex cells combine in fertilization to produce a new individual with the full number of genes — half from each parent. Because the sex cells come in such variety, and come from two parents, there is an enormous number of possible forms for the offspring. (See chromosomes, genetics, and mitosis.)

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Closer Look

Meiosis is the process by which the nucleus divides in all sexually reproducing organisms during the production of spores or gametes. These cells have a single set of chromosomes and are called haploid, as opposed to diploid cells with two sets. In humans, for example, gametes have one set of 23 chromosomes and are formed through meiosis from special diploid cells found in the testes and ovaries. When meiosis begins, each of the 46 chromosomes in these cells consists of two identical chromatids, just as in body cells about to divide by mitosis. However, in meiosis, there are two cell divisions instead of one, so that four daughter cells are produced, instead of two. At the start of the first meiotic division, homologous chromosomes (which have genes for the same traits in the same position) form pairs and exchange genetic material in the process known as crossing over. This process does not occur in mitosis. Then during the first meiotic division, one member of each pair of homologous chromosomes moves to each end of the cell, and the cell itself divides. Each of the two cells produced by the first division has just one set of 23 chromosomes. However, every chromosome still consists of two chromatids at this stage. The two daughter cells then undergo the second meiotic division, which is similar to mitosis. One chromatid from each of the 23 chromosomes moves to each of end of the cell, and the daughter cell itself divides. The chromatids form the chromosomes of the new cells produced by the second meiotic division, and each cell has a single set of 23 chromosomes, normally with slight genetic variation from the original parent cell. In the human female, just one of the four daughter cells will become a functional gamete (the ovum), but in the human male, all four cells develop into gametes (sperm). At fertilization, the union of the male and female gametes restores the two full sets of chromosomes in the human zygote.

Other Word Forms

• meiotic
  adjective
• meiotically
  adverb
• postmeiotic
  adjective

Etymology

Origin of meiosis

1580–90; < Greek meíōsis a lessening, equivalent to meiō-, variant stem of meioûn to lessen (derivative of meíōn less) + -sis -sis

Explanation

The form of cell division that creates gametes, or sex cells (eggs or sperm) is called meiosis. It is a special form of reproduction that results in four next-generation cells, rather than just two, from each cell. As with so many scientific terms, the word meiosis comes from the Greek, in this case meíōsis, which means "a lessening." This idea makes sense, as meiosis creates cells with half the chromosomes than the original. These cells are specifically for reproduction, and then take additional genetic material from the other parent cell. The actual discovery of meiosis happened in 1883, when Belgian scientist Edouard Van Beneden noticed that sex cells had a different way of dividing than did other cells.

Example Sentences

While JQ1 is not suitable as a treatment due to neurological side effects, it is known to interfere with a stage of meiosis called prophase 1.

From Science Daily • Apr. 7, 2026

Cohen and her team focused on meiosis rather than other stages of sperm development to ensure that sperm production could be fully stopped while still allowing it to recover later.

From Science Daily • Apr. 7, 2026

During this time, sperm production stopped completely, and key features of meiosis, including chromosome behavior during prophase 1, were disrupted.

From Science Daily • Apr. 7, 2026

In a proof-of-principle study conducted in mice over six years, the team showed that interrupting a key step in meiosis, the process that produces sex cells, can temporarily halt sperm production without causing lasting harm.

From Science Daily • Apr. 7, 2026

I don’t want to forget what I’ve learned, so I make mental diagrams of the respiratory system, the process of condensation, meiosis and mitosis.

From "The Queen of Water" by Laura Resau