All eukaryotes probably have experienced a polyploidy event at some point in their evolutionary history. Other similar terms
Karyotype
A karyotype is the characteristic chromosome complement of a eukaryote species. The preparation and study of karyotypes is part of cytology and, more specifically, cytogenetics. Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases, there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology. Homoeologous chromosomes
Homoeologous chromosomes are those brought together following inter-species hybridization and allopolyploidization, and whose relationship was completely homologous in an ancestral species. For example, durum wheat is the result of the inter-species hybridization of two diploid grass species Triticum urartu and Aegilops speltoides. Both diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains a hybrid genome with two sets of chromosomes derived from Triticum urartu and two sets of chromosomes derived from Aegilops speltoides. Each chromosome pair derived from the Triticum urartu parent is homoeologous to the opposite chromosome pair derived from the Aegilops speltoides parent, though each chromosome pair unto itself is homologous. Examples
Animals
Examples in animals are more common in non-vertebrates such as flatworms, leeches, and brine shrimp. Within vertebrates, examples of stable polyploidy include the salmonids and many cyprinids (i.e.
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.