Editing Centromere (section)

===Polycentric===
{{Main|Polycentric chromosome}}
Polycentric chromosomes have several kinetochore clusters, i.e. centromes. The term overlaps partially with "holocentric", but "polycentric" is clearly preferred when discussing defectively formed monocentric chromosomes. There is some actual ambiguity as well, as there is no clear line dividing up the transition from kinetochores covering the whole chromosome to distinct clusters. In other words, the difference between "the whole chromosome is a centrome" and "the chromosome has no centrome" is hazy and usage varies. Beyond "polycentricity" being used more about defects, there is no clear preference in other topics such as evolutionary origin or kinetochore distribution and detailed structure (e.g. as seen in [[Fluorescent tag|tagging]] or [[Sequence assembly|genome assembly]] analysis).<ref>{{cite journal | vauthors = Godward MB | date= April 1954 |title=The 'Diffuse' Centromere or Polycentric Chromosomes in Spirogyra |journal=Annals of Botany |volume=18 |issue=2 |pages=143–144 |doi=10.1093/oxfordjournals.aob.a083387 }}</ref><ref name="holocentric_micro">{{cite journal |last1=Kuo |first1=YT |last2=Camara |first2=AS |last3=Schubert |first3=V |title=Holocentromeres can consist of merely a few megabase-sized satellite arrays |journal=Nature Communications |date=2023-06-13 |volume=14 |doi=10.1038/s41467-023-38922-7 |url=https://www.nature.com/articles/s41467-023-38922-7|pmc=10264360 }}</ref><ref name="holocentric_evo">{{cite journal |last1=Senaratne |first1=Aruni P. |last2=Cortes-Silva |first2=Nuria |last3=Drinnenberg |first3=Ines A. |title=Evolution of holocentric chromosomes: Drivers, diversity, and deterrents |journal=Seminars in Cell & Developmental Biology |date=July 2022 |volume=127 |pages=90–99 |doi=10.1016/j.semcdb.2022.01.003 |url=https://www.sciencedirect.com/science/article/pii/S1084952122000052 |access-date=2024-09-11}}</ref><ref name="polycentric_2">{{cite journal |last1=Ma B, Wang H, Liu J, Chen L, Xia X, Wei W, Yang Z, Yuan J, Luo Y, He N. |title=The gap-free genome of mulberry elucidates the architecture and evolution of polycentric chromosomes |journal=Horticulture Research |date=2023-05-31 |volume=10 |issue=7 |doi=10.1093/hr/uhad111 |url=https://pubmed.ncbi.nlm.nih.gov/37786730/ |access-date=2024-09-11|pmc=10541557 }}</ref>

Even clearly distinct clusters of kinetochore proteins do not necessarily produce more than one constriction: "Metapolycentric" chromosomes feature one elongated constriction of the chromosome, joining a longer segment which is still visibly shorter than the chromatids.<ref name="centromere_composition">{{cite journal |last1=Ishii |first1=Midori |last2=Akiyoshi |first2=Bungo |title=Plasticity in centromere organization and kinetochore composition: Lessons from diversity |journal=Current Opinion in Cell Biology |date=February 2022 |volume=74 |issue=Cell Nucleus 2022 |pages=47–54 |doi=10.1016/j.ceb.2021.12.007 |url=https://www.sciencedirect.com/science/article/pii/S0955067422000011#fig3 |access-date=2024-09-11|hdl=20.500.11820/4aab4486-f439-4d7e-863a-b08e0da52a6b |hdl-access=free }}</ref> Metapolycentric chromosomes may be a step in the emergence and suppression of centromere drive, a type of [[meiotic drive]] that disrupts parity by monocentric centromeres growing additional kinetochore proteins to gain an advantage during meiosis.<ref name="centromere_drive">{{cite journal |last1=Zedek |first1=Frantisek |last2=Bures |first2=Petr |title=Absence of positive selection on CenH3 in Luzula suggests that holokinetic chromosomes may suppress centromere drive |journal=Annals of Botany |date=December 2016 |volume=118 |pages=1347–1352 |doi=10.1093/aob/mcw186 |url=https://www.researchgate.net/publication/306091873_Absence_of_positive_selection_on_CenH3_in_Luzula_suggests_that_holokinetic_chromosomes_may_suppress_centromere_drive#read |access-date=2024-09-11|pmc=5155603 }}</ref>