Polyploidy

Having more than two complete sets of chromosomes per cell, common in crops and a major factor in how they can be bred.

• Humans have two sets; potato has four, bread wheat six and cultivated strawberry eight.
• Extra genome copies often give larger cells, fruits and hardiness, and buffer the plant against harmful mutations.
• Many copies make traits hard to fix: a recessive potato trait needs all four copies to match, so breeding is slow and plants are cloned from tubers.
• Breeders are developing two-set hybrid potatoes grown from true seed, which could speed breeding and cut disease spread through tubers.