Octoploids

Octoploids are organisms in which the somatic cells contain eight complete sets of chromosomes, designated 8n. They represent a high level of polyploidy, more common in plants than in animals. Octoploidy can arise through autopolyploidy, such as the doubling of an already polyploid genome (for example, a tetraploid giving rise to an octoploid), or through allopolyploidy, where hybridization between related species is followed by genome doubling to create a stable eight-set genome.

In octoploids, there are eight homologous chromosome sets that must pair during meiosis. This can complicate chromosome pairing and fertilization, so octoploid lineages often rely on mechanisms that promote regular pairing or on asexual reproduction to maintain fertility. The genome is typically highly redundant, which can buffer deleterious mutations and provide raw material for evolutionary diversification through subfunctionalization and neofunctionalization of genes.

Plants show the greatest natural and cultivated incidence of octoploidy. A well-known cultivated example is the strawberry Fragaria × ananassa, which is octoploid (8x) with a chromosome complement of 2n = 8x = 56. Octoploidy has also been observed or engineered in other plant groups to study polyploidization effects and to enhance traits such as size, vigor, or stress tolerance.

Detection and confirmation of octoploidy rely on cytogenetic methods and genome size estimation. Techniques include chromosome counting in root tips, flow cytometry to assess DNA content, and molecular karyotyping. Octoploidy remains relatively rare in natural animal populations compared with plants, where polyploidy is a major driver of diversification and crop improvement.