Editing Polyploidy (section)

==== Humans ====
[[File:Human karyotype with bands and sub-bands.png|thumb|Schematic [[karyotype|karyogram]] of a human, showing the normal [[diploid]] (that is, non-polyploid) [[karyotype]]. It shows 22 [[homologous chromosome]]s, both the female (XX) and male (XY) versions of the [[sex chromosome]] (bottom right), as well as the [[human mitochondrial genetics|mitochondrial genome]] (to scale at bottom left).{{further|Karyotype}}]]
{{Further|Triploid syndrome}}

True polyploidy rarely occurs in humans, although polyploid cells occur in highly [[Cellular differentiation|differentiated]] tissue, such as liver [[parenchyma]], heart muscle, placenta and in bone marrow.<ref name="Velicky2018">{{cite journal | vauthors = Velicky P, Meinhardt G, Plessl K, Vondra S, Weiss T, Haslinger P, Lendl T, Aumayr K, Mairhofer M, Zhu X, Schütz B, Hannibal RL, Lindau R, Weil B, Ernerudh J, Neesen J, Egger G, Mikula M, Röhrl C, Urban AE, Baker J, Knöfler M, Pollheimer J | display-authors = 6 | title = Genome amplification and cellular senescence are hallmarks of human placenta development | journal = PLOS Genetics | volume = 14 | issue = 10 | pages = e1007698 | date = October 2018 | pmid = 30312291 | pmc = 6200260 | doi = 10.1371/journal.pgen.1007698 | doi-access = free }}
</ref><ref>{{cite journal | vauthors = Winkelmann M, Pfitzer P, Schneider W | title = Significance of polyploidy in megakaryocytes and other cells in health and tumor disease | journal = Klinische Wochenschrift | volume = 65 | issue = 23 | pages = 1115–1131 | date = December 1987 | pmid = 3323647 | doi = 10.1007/BF01734832 }}</ref> [[Aneuploidy]] is more common.

Polyploidy occurs in humans in the form of [[Triploid syndrome|triploidy]], with 69 chromosomes (sometimes called 69, XXX), and tetraploidy with 92 chromosomes (sometimes called 92, XXXX). Triploidy, usually due to [[polyspermy]], occurs in about 2–3% of all human pregnancies and ~15% of miscarriages.{{Citation needed|date=November 2009}} The vast majority of triploid conceptions end as a [[miscarriage]]; those that do survive to term typically die shortly after birth. In some cases, survival past birth may be extended if there is [[mixoploidy]] with both a [[diploid]] and a triploid cell population present. There has been one report of a child surviving to the age of seven months with complete triploidy syndrome. He failed to exhibit normal mental or physical neonatal development, and died from a ''[[Pneumocystis carinii]]'' infection, which indicates a weak immune system.<ref>{{cite web|url=https://rarediseases.org/rare-diseases/triploidy/|title=Triploidy|publisher=National Organization for Rare Disorders|language=en-US|access-date=2018-12-23}}</ref>

Triploidy may be the result of either [[digyny]] (the extra haploid set is from the mother) or [[diandry]] (the extra haploid set is from the father). Diandry is mostly caused by reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) [[fertilization]] of the egg.<ref name="Ten Teachers">{{cite book | vauthors = Baker P, Monga A, Baker P |title=Gynaecology by Ten Teachers |publisher=Arnold |location=London |year=2006 |isbn=978-0-340-81662-2 |url-access=registration |url=https://archive.org/details/gynaecology0000unse }}</ref> Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploid [[oocyte]] or failure to extrude one [[polar body]] from the [[oocyte]]. Diandry appears to predominate among early [[miscarriage]]s, while digyny predominates among triploid zygotes that survive into the fetal period.<ref>{{cite journal | vauthors = Brancati F, Mingarelli R, Dallapiccola B | title = Recurrent triploidy of maternal origin | journal = European Journal of Human Genetics | volume = 11 | issue = 12 | pages = 972–974 | date = December 2003 | pmid = 14508508 | doi = 10.1038/sj.ejhg.5201076 | doi-access = free }}</ref> However, among early miscarriages, digyny is also more common in those cases less than {{frac|8|1|2}} weeks gestational age or those in which an embryo is present. There are also two distinct [[phenotype]]s in triploid [[placenta]]s and [[fetus]]es that are dependent on the origin of the extra [[haploid]] set. In digyny, there is typically an asymmetric poorly grown [[fetus]], with marked [[adrenal]] [[hypoplasia]] and a very small [[placenta]].<ref name="pmid23943708">{{cite journal | vauthors = Wick JB, Johnson KJ, O'Brien J, Wick MJ | title = Second-trimester diagnosis of triploidy: a series of four cases | journal = AJP Reports | volume = 3 | issue = 1 | pages = 37–40 | date = May 2013 | pmid = 23943708 | pmc = 3699153 | doi = 10.1055/s-0032-1331378 }}</ref> In diandry, a partial [[hydatidiform mole]] develops.<ref name="Ten Teachers" /> These parent-of-origin effects reflect the effects of [[imprinting (genetics)|genomic imprinting]].{{citation needed|date=December 2010}}

Complete tetraploidy is more rarely diagnosed than triploidy, but is observed in 1–2% of early miscarriages. However, some tetraploid cells are commonly found in chromosome analysis at [[prenatal diagnosis]] and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise during ''in vitro'' cell culture or whether they are also present in placental cells ''in vivo''. There are, at any rate, very few clinical reports of fetuses/infants diagnosed with tetraploidy mosaicism.

[[Mixoploidy]] is quite commonly observed in human preimplantation embryos and includes haploid/diploid as well as diploid/tetraploid mixed cell populations. It is unknown whether these embryos fail to implant and are therefore rarely detected in ongoing pregnancies or if there is simply a selective process favoring the diploid cells.