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What is polyploidy?

Polyploidy is the process of genome doubling that gives rise to organisms with multiple sets of chromosomes. The term ploidy (see glossary for this and other related terms) refers to the number of complete genomes contained in a single cell. In general, polyploid organisms contain a multiple or combination of the chromosome sets found in the same or a closely related diploid species. Polyploidy can arise from spontaneous somatic chromosome duplication, or as a result of non-disjunction of the homologous chromosomes during meiosis resulting in diploid gametes (for review see Ramsey and Schemske, 2002). It can also be artificially induced by treatment with drugs, such as colchicine, which inhibits cell division. Polyploidy can occur in all or most somatic cells of the organism or it can be restricted to a specific tissue. In the latter case the preferred term is endopolyploidy. Some examples of such specialized cells in animals include the salivary gland cells in Drosophila or liver cells in humans.

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Historically, there has been much confusion over whether to classify polyploids by mode of origin criteria or by cytological criteria. Here we follow Ramsey and Schemske (2002) and adopt mode of origin criteria: if the chromosomes of one genome within an organism or species are simply duplicated, the resulting polyploid is an autopolyploid. However, if genome duplication occurs during a cross of two different species, the resulting organism is referred to as an allopolyploid.

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