polyploidization

Polyploidization is the process by which an organism acquires more than two complete sets of chromosomes. It is a major mechanism of genome duplication and is especially common in plants, where it can occur naturally or be induced. Polyploids are organisms with triploid, tetraploid, hexaploid, or higher numbers of chromosome sets, in contrast to the diploid state that dominates most animals and many plants.

There are two principal routes: autopolyploidy and allopolyploidy. Autopolyploidy results when chromosome duplication occurs within a single species, often via nondisjunction or unreduced gametes, producing an individual with more than two homologous chromosome sets. Allopolyploidy arises from hybridization between distinct species followed by chromosome doubling, giving a combined set of homeologous chromosomes that behave as a single genome during meiosis.

Polyploidization can alter cell size, physiology, and morphology. In plants, polyploids often have larger cells and tissues, increased vigor or tolerance to environmental stress, and sometimes altered flowering time. Because of chromosome pairing, fertility in odd-numbered polyploids (such as triploids) can be reduced, while even-numbered polyploids may form stable gametes. Gene redundancy can promote neofunctionalization and subfunctionalization, facilitating genome evolution and potentially rapid speciation, a common occurrence in plants.

In agriculture, polyploidization is exploited to develop new crop varieties. Synthetic polyploids are produced with chemicals such as colchicine to induce chromosome doubling. Well-known crops with polyploid origins include bread wheat (allohexaploid), cotton (allotetraploid), and coffee (allotetraploid). Polyploid studies also illuminate genome evolution and the history of polyploid lineages across taxa.