Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than two copies (ploidy) of their chromosomes. The polyploid types are names 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 abberation, monoploidy may also occur as a normal stage in an organisms life cycle.

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 realted species, the chromosome of allopolyploids are described as homeologus since they are only partially homologous.

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.

External link

• Polyploidy on Kimball's Biology Pages