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. Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm. 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. 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. Humans
True polyploidy rarely occurs in humans, although polyploid cells occur in highly differentiated tissue, such as liver parenchyma, heart muscle, placenta and in bone marrow. 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. The vast majority of triploid conceptions end as a miscarriage; those that do survive to term typically die shortly after birth.
It occurs in the somatic cells of some animals, such as goldfish, salmon, and salamanders, but is especially common among ferns and flowering plants (see Hibiscus rosa-sinensis), including both wild and cultivated species. Wheat, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus Brassica are also tetraploids. Sugarcane can have ploidy levels higher than octaploid.Polyploidization can be a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant Erythranthe peregrina. Sequencing confirmed that this species originated from E. × robertsii, a sterile triploid hybrid between E. guttata and E. lutea, both of which have been introduced and naturalised in the United Kingdom. New populations of E. peregrina arose on the Scottish mainland and the Orkney Islands via genome duplication from local populations of E. × robertsii. Because of a rare genetic mutation, E. peregrina is not sterile. Terminology
Types
Polyploid types are labeled according to the number of chromosome sets in the nucleus.