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Examples in animals are more common in non-vertebrates[41] such as flatworms, leeches, and brine shrimp. Within vertebrates, examples of stable polyploidy include the salmonids and many cyprinids (i.e. carp).[42] Some fish have as many as 400 chromosomes.[42] Polyploidy also occurs commonly in amphibians; for example the biomedically important genus Xenopus contains many different species with as many as 12 sets of chromosomes (dodecaploid).[43] Polyploid lizards are also quite common. Most are sterile and reproduce by parthenogenesis;[citation needed] others, like Liolaemus chiliensis, maintain sexual reproduction. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis,[44] "stealing" spermatophores from diploid males of related species to trigger egg development but not incorporating the males' DNA into the offspring.

While mammalian liver cells are polyploid, rare instances of polyploid mammals are known, but most often result in prenatal death. An octodontid rodent of Argentina's harsh desert regions, known as the plains viscacha rat (Tympanoctomys barrerae) has been reported as an exception to this 'rule'.[45] However, careful analysis using chromosome paints shows that there are only two copies of each chromosome in T. barrerae, not the four expected if it were truly a tetraploid.[46] This rodent is not a rat, but kin to guinea pigs and chinchillas. Its "new" diploid (2n) number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family, whose 2n \= 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 2n \= 4x \= 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.

Polyploidy was induced in fish by Har Swarup (1956) using a cold-shock treatment of the eggs close to the time of fertilization, which produced triploid embryos that successfully matured.[47][48] Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm.[49] John Gurdon (1958) transplanted intact nuclei from somatic cells to produce diploid eggs in the frog, Xenopus (an extension of the work of Briggs and King in 1952) that were able to develop to the tadpole stage.[50] The British scientist J. B. S. Haldane hailed the work for its potential medical applications and, in describing the results, became one of the first to use the word "clone" in reference to animals. Later work by Shinya Yamanaka showed how mature cells can be reprogrammed to become pluripotent, extending the possibilities to non-stem cells. Gurdon and Yamanaka were jointly awarded the Nobel Prize in 2012 for this work.[50]

Polyploidy rarely occurs in humans, although polyploid cells occur in highly differentiated tissue, such as liver parenchyma, heart muscle, placenta and in bone marrow.[2][51] Aneuploidy is more common.

Polyploidy occurs in humans in the form of 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] 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

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