Polyploidy occurs in
cells and
organisms when there are more than two
homologous sets of
chromosomes.
Polyploid types are labelled according to the number of chromosome sets in the
nucleusMost organisms are normally diploid; polyploidy may occur due to abnormal cell division. 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, salmon, and salamanders, but is especially common among ferns and 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 agriculturally important plants of the genus Brassica are also tetraploids; their relationship is described by the Triangle of U.
The occurrence of polyploidy is a mechanism of speciation and is known to have resulted in new species of the plant Salsify (also known as "goatsbeard").
