Origin of meiosis
Examples from the Web for meiosis
Meiosis in Rhynchonympha in one cytoplasmic and two nuclear divisions followed by autogamy.
"A meiosis in common use, equivalent to 'Yes, assuredly,'" murmured the Duke.Zuleika Dobson|Max Beerbohm
Haploid (n) chromosome numbers were determined from cells in diakinesis, metaphase I, and metaphase II of meiosis.Neotropical Hylid Frogs, Genus Smilisca|William E. Duellman
One-division meiosis and autogamy without cell division in Urinympha.
Meiosis in Barbulanympha following fertilization, autogamy, and endomitosis.
British Dictionary definitions for meiosis
noun plural -ses (-ˌsiːz)
Word Origin for meiosis
Word Origin and History for meiosis
"division of a cell nucleus," 1905, from Greek meiosis "a lessening," from meioun "to lessen," from meion "less," from PIE root *mei- "small" (see minus).
Earlier (1580s) it was a rhetorical term, a figure of speech "weak or negative expression used for a positive and forcible one, so that it may be made all the more emphatic," as when one says "not bad" meaning "very good" or "don't mind if I do" meaning "I really would like to," or this example from "Mark Twain":
"YOUNG AUTHOR." -- Yes Agassiz does recommend authors to eat fish, because the phosphorus in it makes brains. So far you are correct. But I cannot help you to a decision about the amount you need to eat,--at least, not with certainty. If the specimen composition you send is about your fair usual average, I should judge that perhaps a couple of whales would be all you would want for the present. Not the largest kind, but simply good, middling-sized whales.
Related: meiotic; meiotically.
Medicine definitions for meiosis
n. pl. mei•o•ses (-sēz′)
Science definitions for meiosis
A 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.
Culture definitions for meiosis
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.)