polyploidi

Polyploidi, or polyploidy, is the condition in which an organism has more than two complete sets of chromosomes. It is especially common in plants, where it has played a major role in evolution and agricultural improvement. In animals, polyploidy occurs less frequently and often involves reproductive barriers or reduced fertility.

Polyploidy arises through two main routes. Autopolyploidy occurs when genome duplication happens within a single species, often via unreduced (diploid) gametes or somatic doubling, leading to individuals with three or more chromosome sets from the same genome. Allopolyploidy results from hybridization between two distinct species, followed by chromosome doubling that restores fertility by allowing pairing between related chromosomes from different parental genomes. In allopolyploids, the combined chromosome sets are typically from different ancestral species, giving a mosaic genome.

The consequences of polyploidy include changes in cell size and physiology, often associated with larger plant organs and altered growth habits. Fertility patterns differ: even-numbered polyploids (tetraploids, hexaploids, etc.) tend to have more regular meiosis and higher fertility, whereas odd-numbered polyploids (triploids) are frequently sterile or partially fertile. Polyploid genomes also exhibit gene redundancy, which can enable neofunctionalization and adaptation to new environments. Polyploidy can drive speciation by creating reproductive isolation between polyploids and their diploid progenitors.

Common polyploid crops include bread wheat (allohexaploid, 6x), cotton (allotetraploid, 2n=4x), potato (autotetraploid, 4x), and strawberry (octoploid, 8x). Detection methods include chromosome counting, flow cytometry to estimate genome size, and genomic sequencing.

In plant breeding, polyploidy is exploited to create new varieties and traits, including seedless fruit through triploidy and increased vigor through genome duplication.