Tetraploidy

Tetraploidy refers to the state of having four complete sets of chromosomes in a cell or organism, typically described as 4n or 4x, compared with the diploid number (2n) found in most sexually reproducing species. Tetraploidy can arise in several ways, most commonly by genome duplication within a species (autopolyploidy) or by hybridization between two species followed by chromosome doubling (allopolyploidy). Other routes include endoreduplication, where a somatic cell duplicates its genome without cell division.

In meiosis, tetraploid organisms face challenges in homologous chromosome pairing, which can reduce fertility in autopolyploids. Double reduction and multivalent formation can occur, but tetraploids that arise through allopolyploidy often show more regular meiosis because their subgenomes behave as homologous chromosomes within separate chromosome sets. Polyploidization can immediately create reproductive isolation and in plants is a major mechanism of speciation.

Tetraploidy is common in plants and is utilized in agriculture and horticulture. Many crop species exist as tetraploids or include tetraploid varieties, such as tetraploid potato and tetraploid forms of durum wheat or Brassica napus. In vertebrates, tetraploidy is rare but occurs in some lineages, such as the allotetraploid amphibian Xenopus laevis; in mammals, polyploid cells commonly arise by endoreduplication in tissues like liver and placenta.

Detection and study rely on cytogenetic methods and DNA content analysis, including karyotyping and flow cytometry. Tetraploidy has implications for cell size, gene dosage, and phenotype, and it contributes to variation and adaptation in plant populations and, in some cases, to evolutionary diversification.