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Volvox carteri
''Volvox carteri'' F.Stein 1873 is a species of colonial green algae in the order Volvocales. ''V. carteri'' forms large spherical colonies, or coenobium, of 2000-6000 ''Chlamydomonas'' type cells. Colonies contain mostly somatic cells plus a smaller number of gametes in female or male colonies.〔 In addition to female colonies with eggs and male colonies with sperm bundles, purely vegetative colonies exist.〔 All three types of colonies may also have specialized cells called gonidia for asexual reproduction of the colony.〔
The genome of this species of algae was sequenced in 2010.
==Sexual reproduction==
''V. carteri'' can reproduce either asexually or sexually. Thus, it is a facultatively sexual organism. In nature, Volvox reproduces asexually in temporary ponds in spring, but becomes sexual and produces dormant over-wintering zygotes before the ponds dry up in the summer heat. ''V. carteri'' can be induced to reproduce sexually by heat shock treatment. However, this induction can be inhibited by antioxidants indicating that the induction of sex by heat shock is mediated by oxidative stress. Nedelcu et al. further found that an inhibitor of the mitochondrial electron transport chain that induces oxidative stress also induced sex in ''V. carteri''. Nedelcu and Michod〔 and Nedelcu et al.〔 suggested that oxidative DNA damage caused by oxidative stress may be the underlying cause of the induction of sex in their experiments. Other agents that cause DNA damage (i.e. glutaraldehyde, formaldehyde and UV) also induce sex in ''V. carteri''.〔Starr RC, Jaenicke L. (1988). Sexual induction in Volvox carteri f. nagariensis by aldehydes. Sex Plant Reprod 1:28-31.〕 These findings lend support to the general idea that a principal adaptive function of sex is repair of DNA damages.〔Birdsell JA, Wills C (2003). The evolutionary origin and maintenance of sexual recombination: A review of contemporary models. Evolutionary Biology Series >> Evolutionary Biology, Vol. 33 pp. 27-137. MacIntyre, Ross J.; Clegg, Michael, T (Eds.), Springer. Hardcover ISBN 978-0306472619, ISBN 0306472619 Softcover ISBN 978-1-4419-3385-0.〕
〔Bernstein H, Bernstein C, Michod RE (2012). DNA repair as the primary adaptive function of sex in bacteria and eukaryotes. Chapter 1: pp.1-49 in: DNA Repair: New Research, Sakura Kimura and Sora Shimizu editors. Nova Sci. Publ., Hauppauge, N.Y. ISBN 978-1-62100-808-8 https://www.novapublishers.com/catalog/product_info.php?products_id=31918〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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