Editing Ploidy (section)

===Ancestral ploidy levels===
It is possible on rare occasions for ploidy to increase in the [[germline]], which can result in [[polyploid]] offspring and ultimately polyploid species. This is an important evolutionary mechanism in both plants and animals and is known as a primary driver of [[speciation]].<ref name="Mable-2004"/> As a result, it may become desirable to distinguish between the ploidy of a species or variety as it presently breeds and that of an ancestor. The number of chromosomes in the ancestral (non-homologous) set is called the '''monoploid number''' (''x''), and is distinct from the haploid number (''n'') in the organism as it now reproduces.{{citation needed|date=May 2023}}

[[Common wheat]] (''Triticum aestivum'') is an organism in which ''x'' and ''n'' differ. Each plant has a total of six sets of chromosomes (with two sets likely having been obtained from each of three different diploid species that are its distant ancestors). The somatic cells are hexaploid, 2''n''&nbsp;=&nbsp;6''x''&nbsp;=&nbsp;42 (where the monoploid number ''x''&nbsp;=&nbsp;7 and the haploid number ''n''&nbsp;=&nbsp;21). The gametes are haploid for their own species, but triploid, with three sets of chromosomes, by comparison to a probable evolutionary ancestor, [[einkorn wheat]].{{citation needed |date=March 2017}}

[[Tetraploidy]] (four sets of chromosomes, 2''n''&nbsp;=&nbsp;4''x'') is common in many [[plant]] species, and also occurs in [[amphibian]]s, [[reptile]]s, and [[insect]]s. For example, species of ''[[Xenopus]]'' (African toads) form a '''ploidy series''', featuring diploid (''[[Western clawed frog|X. tropicalis]]'', 2n=20), tetraploid (''[[African clawed frog|X. laevis]]'', 4n=36), octaploid (''[[De Witte's clawed frog|X. wittei]]'', 8n=72), and dodecaploid (''[[Uganda clawed frog|X. ruwenzoriensis]]'', 12n=108) species.<ref>{{cite journal |last1=Schmid |first1=M |last2=Evans |first2=BJ |last3=Bogart |first3=JP |title=Polyploidy in Amphibia |journal=Cytogenet. Genome Res. |date=2015 |volume=145 |issue=3–4 |pages=315–330 |doi=10.1159/000431388 |pmid=26112701|doi-access=free }}</ref>

Over evolutionary time scales in which [[chromosomal polymorphism]]s accumulate, these changes become less apparent by [[karyotype]] – for example, humans are generally regarded as diploid, but the [[2R hypothesis]] has confirmed two rounds of whole genome duplication in early vertebrate ancestors.{{cn|date=June 2024}}