Allotetraploids

An allotetraploid is a polyploid organism carrying four sets of chromosomes derived from two different species. It typically forms when two distinct diploid species hybridize to produce an interspecific hybrid that then undergoes genome doubling, yielding a stable, fertile allotetraploid with two distinct subgenomes, often referred to as A and B (AABB).

During meiosis, chromosomes tend to pair with their true homolog within the same subgenome (disomic inheritance), which preserves fertility and stabilizes the genome. Although the subgenomes largely segregate, limited homoeologous recombination and chromosomal rearrangements can occur, contributing to variation and adaptation.

Allotetraploids are common in plants and include agriculturally important crops such as durum wheat (Triticum turgidum; AABB) and upland cotton (Gossypium hirsutum; AADD). They also occur in natural systems, such as Tragopogon miscellus and Tragopogon mirus, examples that have provided key insights into polyploid evolution and speciation.

Formation mechanisms include unreduced gametes and somatic chromosome doubling; polyploidy can act as a barrier to hybrid sterility and promote ecological diversification. Allotetraploidy contrasts with autopolyploidy, where the genome doubles within a single species.