Allopolyploid

An allopolyploid is a polyploid organism whose chromosome sets come from two or more different species. It arises when individuals from distinct species hybridize and the resulting hybrid undergoes chromosome doubling, restoring fertility and enabling proper chromosome pairing during meiosis. The genome typically consists of distinct subgenomes that behave as separate but coexisting chromosome sets, leading to disomic inheritance rather than the random pairing seen in autopolyploids.

Formation many times involves interspecific hybridization followed by genome doubling, which can occur spontaneously or be induced by chemicals such as colchicine. The process creates a new, stable lineage that combines genetic material from the parent species, often facilitating novel trait combinations and ecological divergence.

Characteristics and consequences include pairing of homologous chromosomes within each subgenome, reduced sterility in the hybrid, and potential subgenome dominance where one ancestor’s genes are more highly expressed. Over time, duplicate genes may be retained, diverge in function, or become silenced, and epigenetic changes can occur as the genome stabilizes.

Examples and importance: bread wheat, Triticum aestivum, is an allohexaploid with AABBDD genomes. Brassica napus (canola) is an allotetraploid with AACC. Upland cotton, Gossypium hirsutum, is allotetraploid with AADD. Triticale is an allohexaploid derived from wheat and rye with AABBRR genomes. Allopolyploidy is a major driver of plant speciation, offering novel trait combinations and increased adaptability, and it has been central to agricultural crop improvement.