octoploidy

Octoploidy is a form of polyploidy in which an organism has eight complete sets of chromosomes in its cells (8n). This genomic state is most commonly observed in plants and arises through whole-genome duplication or hybridization between species followed by chromosome doubling. Octoploids can form by autopolyploidy, when unreduced (2n) gametes fuse, or by allopolyploidy, when the genomes of different species merge and stabilize as eight homologous chromosome sets.

In plants, octoploidy is a well-documented condition and can be associated with increased cell size, growth vigor, and altered development. The cultivated strawberry, Fragaria × ananassa, is a prominent allo-octoploid with 56 chromosomes. Other octoploid lineages have been described in various plant groups, including some ferns and orchids. In animals, octoploidy is rare and less well characterized; when it occurs, it is typically accompanied by reproductive barriers and developmental changes that can hinder fertility.

Meiosis in octoploids presents challenges because eight homologous chromosomes must pair and segregate properly. Successful octoploid lineages often require genomic stabilization and regulatory adjustments that balance gene expression across the eight chromosome sets. Despite these complexities, octoploidy can contribute to phenotypic novelty and ecological or agricultural adaptation, particularly in crops where polyploidy is exploited for desirable traits.

Significance: octoploidy expands genetic diversity and may enable new trait combinations, but it also complicates breeding and genome management due to increased chromosome number and intricate pairing behavior during meiosis.