Polyploidy

n. (Biology) state of having three or more times the normal number of chromosomes (about cells)

Polyploidy is the condition of some biological cells and organisms manifested by the presence of more than two homologous sets of chromosomes. Polyploid types are termed according to the number of chromosome sets in the nucleus: triploid (three sets; 3x), tetraploid (four sets; 4x), pentaploid (five sets; 5x), hexaploid (six sets; 6x) and so on.
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Noun
1. the condition of being polyploid
(hypernym) condition

The situation in which the organism has more than two (2n) sets of chromosomes. It could be 3n, 4n or more. A common situation in earthworms and plants. About half of angiosperms are polyploid. It arises as a result of meiotic irregularities and gives rise to sterile progeny which can still reproduce asexually. The original South American potato is a tetraploid (4n). Many of the common food plants are polyploid as this results in larger flowers and fruits (as well as larger cells, thicker and fleshier leaves). The wheat now grown for bread T. aestivum is hexaploid (6n = 42 chromosomes). Polyploidy is a common mechanism for sympatric speciation which played a role in angiosperm evolution. Link to a mini-essay on polyploidy .

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