Somatic genome-doubling is the most parsimonious route to allopolyploidy

The origin of a polyploid can hinge on a single errant cell division, a mistake in the cell cycle that leads to genome-doubling and re-writes the rules of chromosome pairing and segregation. In plants, the evolutionary significance of these errors is magnified by lack of an early sequestered germline, meaning somatic mutations can be heritable. For sterile hybrids, somatic genome-doubling can be an immediate beneficial mutation, providing each chromosome with a homolog for pairing during meiosis, partially restoring fertility. This review examines evidence for the origin of polyploid hybrids, known as allopolyploids. While the involvement of unreduced gametes or triploid bridges remains plausible, both natural and synthetic allopolyploids indicate that somatic genome-doubling following hybridization is the most parsimonious route.