Tetraploïd

Tetraploïd, or tetraploid, refers to an organism or cell that contains four complete sets of chromosomes (4n, 4x). This ploidy level arises through whole-genome duplication or hybridization events and is especially common in plants, though it occurs in some animal groups as well.

There are two main routes to tetraploidy. Autopolyploidy results from the duplication of a species’ own genome, often via unreduced gametes or somatic chromosome doubling. Allopolyploidy occurs when two related species hybridize and the resulting hybrid subsequently doubles its chromosomes, producing a stable chromosome complement from two distinct genomes. In both cases, errors in chromosome segregation during meiosis or mitosis can contribute to the formation of a four-set state.

Consequences of tetraploidy include changes in cell size and often in organ size, which can influence plant morphology and vigor. Fertility and meiotic behavior differ between auto- and allopolyploids; autopolyploids may experience multivalent chromosome pairing that reduces fertility unless corrective pairing occurs, while allopolyploids can benefit from pairing between homoeologous chromosomes. Tetraploidy can also drive reproductive isolation and contribute to speciation, as chromosome number differences impede back-crossing with diploid relatives.

Examples of tetraploidy are found in several crops and lineages. Tetraploid wheat (Triticum turgidum) and allotetraploid cotton (Gossypium hirsutum) illustrate agricultural relevance. Potatoes (Solanum tuberosum) and some sugarcane varieties also display tetraploid or higher polyploid states. Detection methods include chromosome counting and flow cytometry to estimate DNA content, complemented by molecular and genomic analyses.

Overall, tetraploïd represents a key mechanism of genome evolution with wide-ranging implications for biology and agriculture.