Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than two copies (ploidy) of their chromosomes. The polyploid types are termed triploid (3x), tetraploid (4x), pentaploid (5x), hexaploid (6x) and so on. Where an organism is normally diploid, a monoploid (1x) may arise as a spontaneous aberration; monoploidy may also occur as a normal stage in an organism's life cycle. Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... In biology and ecology, an organism (in Greek organon = instrument) is an assembly of molecules that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Ploidy indicates the number of copies of the basic number of chromosomes. ... Figure 1: Chromosome. ...

Autopolyploids are composed of multiple sets of chromosomes from within one species, while allopolyploids are composed of chromosome sets from different species. Allopolyploids usually only form between closely related species, the chromosome of allopolyploids is described as homeologus since they are only partially homologous. Amphidiploid and allotetraploid mean having two chromosome sets from one species and two chromosome sets from another species. These are formed from the hybridisation of two separate species followed by their subsequent chromosome doubling.

Polyploidy occurs in animals but is especially common among flowering plants, 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 plants from the genus Brassica also show interesting inter-specific allotetraploids; the relationship is described by the Triangle of U. Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... Divisions Green algae Land plants (embryophytes) Non-vascular embryophytes Hepatophyta - liverworts Anthocerophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Seedless vascular plants Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... In biology, a species is a kind of organism. ... Species T. boeoticum T. durum T. monococcum T. spelta References:   ITIS 42236 2002-09-22 Wheat (Triticum spp. ... In genetics, hybridisation is the process of mixing different species or varieties of organisms. ... Durum wheat (Triticum turgidum durum) is the only tetraploid species of wheat widely cultivated today. ... Macaroni is typically machine-made dry commercial pasta, used in contrast to fresh pasta made at home or in small local businesses. ... Species See text Brassica is a plant genus, in the cabbage family (Cruciferae, also known, more fashionably, as the Brassicaceae). ... The Triangle of U is a theory which describes the evolution and relationships between members of the plant genus Brassica. ...

Examples in animals are more common in the ‘lower’ forms such as flatworms, leeches, and brine shrimps. Reproduction is often by parthenogenesis (asexual reproduction by a female) since the polyploids are often sterile. Polyploid salamanders and lizards are also quite common and parthenogenetic. Kaguya is one success from 460 attempts at growing embryos. ...

Triploids are always sterile since one third of the chromosomes cannot pair. This trait has been exploited commercially in both animals and plants. The popular seedless watermelons are triplods and the advantage of sterility in this case is clear. Farmed oysters are also triploid and have a less clear advantage over the diploid wild species. The diploids have a spawning season and during this time they taste bad, however, since the triploids are sterile they do not spawn and are never out of season.

Polyploidy can be induced in cell culture by some chemicals: the best known is colchicine, which causes chromosome doubling. A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... Colchicine is a highly poisonous alkaloid, originally extracted from plants of the genus Colchicum (autumn crocus, meadow saffron) with the chemical formula C22H25NO6. ...

External link

• Polyploidy on Kimball's Biology Pages