allooctoploid

An allooctoploid, or allo-octoploid, is an organism whose somatic cells contain eight complete sets of chromosomes derived from different species. In general, the eight chromosome sets are organized into distinct subgenomes, reflecting hybrid origin from multiple ancestors. The base chromosome number of a given lineage is denoted x, so an allooctoploid has 8x chromosomes in its somatic cells (for example, if x equals 7, 8x equals 56).

Origin and formation typically involve interspecific hybridization between related species followed by genome doubling, or the fusion of unreduced gametes, with one or more subsequent hybridization events contributing additional subgenomes. Such processes create a mosaic genome that combines traits from several lineages.

Genomic structure and inheritance in allooctoploids often exhibit disomic behavior, with chromosome pairing occurring mainly between homologous chromosomes within each subgenome. This can stabilize meiosis relative to more interwoven polyploids, though initial hybrids may experience reduced fertility and genomic instability. Over time, structural rearrangements and chromosomal sorting can further stabilize the genome, aiding fertility and trait expression.

Examples and significance: The cultivated garden strawberry, Fragaria × ananassa, is a well-known allo-octoploid with a 56-chromosome genome derived from multiple Fragaria species. Allooctoploids are of interest in plant breeding because they can combine desirable traits from several progenitors, such as disease resistance, vigor, or fruit quality. They are relatively rare compared with lower ploidies but occur in various plant groups.

Notes: The term highlights origin from distinct species (allo-); by contrast, autopolyploids arise from genome duplication within a single species.