Editing Centromere (section)

=== Holocentric ===
{{Main|Holocentric chromosome}}
Unlike monocentric chromosomes, holocentric chromosomes have no distinct primary constriction when viewed at mitosis. Instead, spindle fibers attach along almost the entire (Greek: holo-) length of the chromosome. In holocentric chromosomes centromeric proteins, such as [[CENPA]] (CenH3) are spread over the whole chromosome.<ref name="mono">{{cite journal | vauthors = Neumann P, Navrátilová A, Schroeder-Reiter E, Koblížková A, Steinbauerová V, Chocholová E, Novák P, Wanner G, Macas J | display-authors = 6 | title = Stretching the rules: monocentric chromosomes with multiple centromere domains | journal = PLOS Genetics | volume = 8 | issue = 6 | pages = e1002777 | year = 2012 | pmid = 22737088 | pmc = 3380829 | doi = 10.1371/journal.pgen.1002777 | doi-access = free }}</ref> The nematode, [[Caenorhabditis elegans]], is a well-known example of an organism with holocentric chromosomes,<ref>{{cite journal | vauthors = Dernburg AF | title = Here, there, and everywhere: kinetochore function on holocentric chromosomes | journal = The Journal of Cell Biology | volume = 153 | issue = 6 | pages = F33–F38 | date = June 2001 | pmid = 11402076 | pmc = 2192025 | doi = 10.1083/jcb.153.6.F33 }}</ref> but this type of centromere can be found in various species, plants, and animals, across eukaryotes. Holocentromeres are actually composed of multiple distributed centromere units that form a line-like structure along the chromosomes during mitosis.<ref>{{cite journal | vauthors = Marques A, Ribeiro T, Neumann P, Macas J, Novák P, Schubert V, Pellino M, Fuchs J, Ma W, Kuhlmann M, Brandt R, Vanzela AL, Beseda T, Šimková H, Pedrosa-Harand A, Houben A | display-authors = 6 | title = Holocentromeres in Rhynchospora are associated with genome-wide centromere-specific repeat arrays interspersed among euchromatin | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 44 | pages = 13633–13638 | date = November 2015 | pmid = 26489653 | pmc = 4640781 | doi = 10.1073/pnas.1512255112 | bibcode = 2015PNAS..11213633M | doi-access = free }}</ref> Alternative or nonconventional strategies are deployed at meiosis to achieve the homologous chromosome pairing and segregation needed to produce viable gametes or gametophytes for sexual reproduction.

Different types of holocentromeres exist in different species, namely with or without centromeric repetitive DNA sequences and with or without [[CENPA|CenH3]]. Holocentricity has evolved at least 13 times independently in various green algae, protozoans, invertebrates, and different plant families.<ref>{{cite journal | vauthors = Melters DP, Paliulis LV, Korf IF, Chan SW | title = Holocentric chromosomes: convergent evolution, meiotic adaptations, and genomic analysis | journal = Chromosome Research | volume = 20 | issue = 5 | pages = 579–593 | date = July 2012 | pmid = 22766638 | doi = 10.1007/s10577-012-9292-1 | s2cid = 3351527 | doi-access = free }}</ref> Contrary to monocentric species where acentric fragments usually become lost during cell division, the breakage of holocentric chromosomes creates fragments with normal spindle fiber attachment sites.<ref>{{Cite journal | author1 = Hughes-Schrader S| author-link1 =Sally Hughes-Schrader| author2 =Ris H |date=August 1941 |title=The diffuse spindle attachment of coccids, verified by the mitotic behavior of induced chromosome fragments |url=https://onlinelibrary.wiley.com/doi/10.1002/jez.1400870306 |journal=Journal of Experimental Zoology |language=en |volume=87 |issue=3 |pages=429–456 |doi=10.1002/jez.1400870306 |issn=0022-104X}}</ref> Because of this, organisms with holocentric chromosomes can more rapidly evolve karyotype variation, able to heal fragmented chromosomes through subsequent addition of telomere caps at the sites of breakage.<ref>{{cite journal | vauthors = Jankowska M, Fuchs J, Klocke E, Fojtová M, Polanská P, Fajkus J, Schubert V, Houben A | display-authors = 6 | title = Holokinetic centromeres and efficient telomere healing enable rapid karyotype evolution | journal = Chromosoma | volume = 124 | issue = 4 | pages = 519–528 | date = December 2015 | pmid = 26062516 | doi = 10.1007/s00412-015-0524-y | s2cid = 2530401 }}</ref>