Allooctoploids

Allooctoploids are allopolyploids with eight sets of chromosomes derived from more than one species. The term combines allo- (other genomes) and octoploid (eight full chromosome sets). In these organisms, the eight chromosome complements may be organized as four pairs of homologous subgenomes, often designated as AABBCCDD.

The most familiar example is the cultivated strawberry Fragaria × ananassa, an allo-octoploid with 2n=56 (x=7), thought to arise from hybridization among four diploid Fragaria progenitors followed by genome doubling. This pattern of four divergent ancestral genomes present in duplicated fashion is typical of allo-octoploids, though exact parental lineages vary among taxa.

Formation occurs via allopolyploidization, such as interspecific crosses followed by chromosome doubling, or through successive hybridization and polyploidization events. Unreduced gametes can contribute to rapid formation. Allo-octoploids often show disomic inheritance, with chromosome pairing largely restricted to homologs from the same subgenome, though imperfect pairing and rearrangements can occur.

Genomic redundancy fosters heterozygosity, potential novelty in traits, and increased environmental tolerance, but also genomic instability and complex gene regulation. Subgenome dominance and epigenetic reprogramming may shape expression patterns. Breeding and genetic analysis are more challenging due to large, compartmentalized genomes.

Allooctoploids are of interest in plant evolution and agriculture, providing insights into polyploid speciation and offering diverse genetic material for crop improvement.