Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than one copy (ploidy) of their chromosomes. 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.
Polyploidy can be induced in cell culture by some chemicals: the best known is colchicine, which causes chromosome doubling.
These are 1) the origin of polyploids, 2) the establishment and coexistence of polyploids in diploid populations, and 3) the spread of polyploids into habitats not occupied by their diploid progenitors.
A problematic and critical step in polyploid evolution is the establishment, and subsequent persistence, of the polyploid (Fowler and Levin, 1984).
Polyploids are known, in general, to have higher stress tolerances and therefore may occupy separate habitats from their diploid ancestors (Levin, 1983).
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