Polyploid

Polyploid is a term used in genetics and biology to describe organisms that possess more than two complete sets of chromosomes. In contrast to diploidy, polyploidy results from whole-genome duplication or interspecific hybridization, and it is especially common in plants, where it can drive speciation and adaptation. Autopolyploidy refers to chromosome duplication within a single species, producing identical chromosome sets. Allopolyploidy results from hybridization between two species followed by chromosome doubling, creating a new, fertile lineage with two distinct chromosome sets from each parent. Polyploidy can arise by unreduced gametes, nondisjunction during cell division, or somatic doubling.

The consequences include changes in cell size and organ size, altered development, and often altered fertility. Even-numbered polyploids can form regular meiosis and be fertile, while odd-numbered polyploids are frequently sterile, which can contribute to reproductive isolation and instant speciation. Polyploid plants are widespread and economically important, with many crops being polyploid; benefits include increased vigor and stress tolerance in some cases, as well as larger fruit or tubers.

Notable examples include bread wheat, Triticum aestivum, a hexaploid with six chromosome sets; cultivated cotton, Gossypium hirsutum, a tetraploid; and potato, Solanum tuberosum, also tetraploid. Bananas and certain other fruits are often triploid and sterile, yet they are cultivated widely for fruit production. Polyploidy remains a key mechanism in plant evolution and agriculture, illustrating how genome duplication can influence form, function, and diversity.