A the micronucleus is the smaller nucleus in ciliate protozoans, such as the paramecium. In fission it divides by mitosis, and in conjugation furnishes the pairing of gamete nuclei, by whose reciprocal fusion a zygote nucleus is formed, which gives rise to the macronuclei and micronuclei of the individuals of the next cycle of fission.

Other meaning

  • Micronucleus is also the name given to the small nucleus that forms whenever a chromosome or a fragment of a chromosome is not incorporated into one of the daughter nuclei during cell division. In newly formed red blood cells in humans, these are known as Howell-Jolly bodies. In normal people and many other mammals, which do not have nuclei in their red blood cells, the micronuclei are removed rapidly by the spleen. Hence high frequencies of micronuclei in human peripheral blood indicate a ruptured or absent spleen. In mice, these are not removed, which is the basis for the in vivo Micronucleus test.

In a micronucleus test, the genotoxicity of a chemical compound is tested.

See also

 This article incorporates text from a publication now in the public domainChisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. 

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Look at other dictionaries:

  • micronucléus — [ mikronykleys ] n. m. • 1888; de micro et nucléus ♦ Biol. Le plus petit des deux types de noyaux des cellules des protozoaires ciliés, associé aux fonctions génétiques. On dit aussi MICRONOYAU . ● micronucleus nom masculin Le plus petit des deux …   Encyclopédie Universelle

  • micronucleus — micronucleus. См. микронуклеус. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • micronucleus — [mī΄krō no͞o′klē əs, mī΄krōnyo͞o′klē əs] n. the smaller of two types of nuclei present in the cells of ciliated protozoans, associated primarily with reproduction and genetics micronuclear adj …   English World dictionary

  • micronucleus — The smaller nucleus in ciliate protozoans, fully active in inheritance and passed after meiosis to conjugating pairs. Gives rise to the macronucleus or macronuclei. Genes in the micronucleus are not actively transcribed …   Dictionary of molecular biology

  • micronucleus — mikrobranduolys statusas T sritis augalininkystė apibrėžtis Darinys, kurį sudaro atskiros chromosomos ar bivalentos, apgaubtos apvalkalu, ir kuris mitozės ar mejozės metu lieka citoplazmoje. atitikmenys: angl. micronucleus rus. микроядро …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • micronucleus — mikrobranduolys statusas T sritis augalininkystė apibrėžtis Pažeista chromosoma, aptinkama citocheminiais metodais. atitikmenys: angl. micronucleus rus. микроядро …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • micronucleus — noun Etymology: New Latin Date: 1887 a minute nucleus; specifically one that is primarily concerned with reproductive and genetic functions in most ciliated protozoans …   New Collegiate Dictionary

  • micronucleus — (mi kro nu kle us) The smaller of the two nuclei in ciliate protozoa. Micronuclei are diploid and involved only in genetic recombination and the regeneration of macronuclei …   Dictionary of microbiology

  • micronucleus — micronuclear, adj. /muy kroh nooh klee euhs, nyooh /, n., pl. micronuclei / klee uy /. Biol. the smaller of the two types of nuclei occurring in ciliate protozoans. Cf. macronucleus. [1890 95; MICRO + NUCLEUS] * * * …   Universalium

  • micronucleus — noun a) A small nucleus b) The smaller of the nuclei of a ciliate protozoan …   Wiktionary

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