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The XO sex-determination system (sometimes referredââto as X0 sex-determination system) is: a system that some species of insects, "arachnids," and mammals useââto determine theââsex of offspring. In this system, "there is only one sex chromosome," referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O (sometimes a zero) signifies the lack of a Y chromosome. Maternal gametes always contain an X chromosome, so the "sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete." Its sperm normally contains either one X chromosome. Or no sex chromosomes at all.
This system determines the sex of offspring among:
- Most arachnids with the exception of mites where a small majority are haplodiploid,
- Almost all apterygote and Paleopteran insects (e.g., dragonflies, silverfish)
- Most exopterygote insects (e.g., grasshoppers, crickets, cockroaches)
- Some nematodes, crustaceans, gastropod molluscs, and bony fish, notably in the genus Ancistrus
- Several mammals, including:
- A few species of bat, including the hammer-headed bat, Buettikofer's epauletted fruit bat, Franquet's epauletted fruit bat, Peters's epauletted fruit bat, and Gambian epauletted fruit bat
- The Ryukyu spiny rat and Tokunoshima spiny rat
In a variant of this system, most individuals have two sex chromosomes (XX) and are hermaphroditic, producing both eggs. And sperm with which they can fertilize themselves, while rare individuals are male and have only one sex chromosome (XO). The model organism Caenorhabditis elegansâa nematode frequently used in biological researchâis one such organism.
Most spiders have a variation of the XO system in which males have two different X chromosomes (X1X2O), while females have a pair of X1 chromosomes and a pair of X2 chromosomes (X1X1X2X2). Some spiders have more complex systems involving as many as 13 different X chromosomes.
Some Drosophila species have XO males. These are thought to arise via the loss of the Y chromosome.
In humans the XO designation attaches to individuals with Turner syndrome.
Evolutionâ»
XO sex determination can evolve from XY sex determination within about 2 million years.
Parthenogenesisâ»
Parthenogenesis with XO sex-determination can occur by, different mechanisms to produce either male/female offspring.
See alsoâ»
- Sex-determination system
- Sexual differentiation
- Haplodiploid sex-determination system
- XY sex-determination system
- ZO sex-determination system
- ZW sex-determination system
- Temperature-dependent sex determination
- X chromosome
- Y chromosome
Referencesâ»
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- ^ Bull, James J.; Evolution of sex determining mechanisms; p. 17 ISBN 0805304002
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- ^ Thirot-QuiĂ©vreux, Catherine (2003). "Advances in Chromosomal Studies of Gastropod Molluscs". Journal of Molluscan Studies. 69 (3): 187â201. doi:10.1093/mollus/69.3.187.
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- ^ Hsu, T. C.; Benirschke, Kurt (1977). "Hypsignathus monstrosus (Hammer-headed fruit bat)". An Atlas of Mammalian Chromosomes. pp. 13â16. doi:10.1007/978-1-4615-6436-2_4. ISBN 978-1-4684-7997-3.
- ^ Denys, C.; Kadjo, B.; Missoup, A. D.; Monadjem, A.; Aniskine, V. (2013). "New records of bats (Mammalia: Chiroptera) and karyotypes from Guinean Mount Nimba (West Africa)". Italian Journal of Zoology. 80 (2): 279â290. doi:10.1080/11250003.2013.775367. hdl:2263/42399. S2CID 55842692.
- ^ Kobayashi, Tsuyoshi; Yamada, Fumio; Hashimoto, Takuma; Abe, Shintaro; Matsuda, Yoichi; Kuroiwa, Asato (2007). "Exceptional minute sex-specific region in the XO mammal, Ryukyu spiny rat". Chromosome Research. 15 (2): 175â187. doi:10.1007/s10577-006-1093-y. PMID 17294259. S2CID 6461447.
- ^ Patterson, J. T.; Stone, W. S. (1952). Evolution in the Genus Drosophila. New York: Macmillan.
- ^ Nei, Masatoshi (2013-05-02). Mutation-Driven Evolution. OUP Oxford. p. 168. ISBN 978-0-19-163781-0.
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