Polyploidy

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Polyploidy occurs in cells and organisms when there are more than two paired (homologous) sets of chromosomes.

Most organisms are normally diploid, meaning they have two sets of chromosomes — one set inherited from each parent. Polyploidy may occur due to abnormal cell division during metaphase I in meiosis. It is most commonly found in plants. (Haploidy may also occur as a normal stage in an organism's life. A haploid has only one set of chromosomes.)

Polyploidy occurs in some animals, such as goldfish,[1] 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; their relationship is described by the Triangle of U.

Polyploidy also occurs normally in some animal tissues, such as human muscle tissues.[2] This is known as endopolyploidy.

The occurrence of polyploidy is a mechanism of speciation and is known to have resulted in new species of the plant Salsify (Tragopogon).

Polyploidy can be induced in plants and cell cultures by some chemicals: the best known is colchicine, which can result in chromosome doubling, though its use may have other less obvious consequences as well. Oryzalin also will double the existing chromosome content.

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