Alloploidi

Alloploidi, or allopolyploidy, is a form of polyploidy that arises when two distinct species hybridize and the resulting hybrid undergoes chromosome doubling or stabilizes its genome, producing an organism with complete chromosome sets from different species. In allopolyploids, each subgenome retains its own set of chromosomes, and the combined genome often behaves as a mosaic of parental genomes.

A key feature of allopolyploids is that pairing during meiosis tends to occur between homologous chromosomes within the same subgenome, rather than between homeologous chromosomes from different species. This can restore fertility to a sterile hybrid by enabling balanced gamete formation. Fertility is commonly achieved through genome doubling, which creates homologous chromosome pairs for each subgenome. Allopolyploid formation can occur via unreduced (diploid) gametes or somatic chromosome doubling followed by reproduction.

Allopolyploidy is widespread in plants and has played a major role in crop domestication and plant diversification. Notable examples include bread wheat (Triticum aestivum), an allohexaploid with genomes AABBDD derived from three ancestral species; Brassica napus (canola), an allotetraploid with AACC from distinct Brassica lineages; and many polyploid cotton species that combine A and D subgenomes. Allopolyploids often exhibit novel traits, such as increased size, environmental tolerance, or heterosis, and can undergo gene expression changes and epigenetic remodeling that influence phenotype.

In contrast to autopolyploidy, which involves genome duplication within a single species, allopolyploidy creates multiple, distinct subgenomes within a single organism, contributing to genetic diversity and speciation.