Bread wheat is three grasses that never came apart

The wheat in a loaf carries three complete ancestral genomes. Two wild hybridisations stacked them, and the plant kept all three instead of choosing.

Bread wheat, Triticum aestivum, is hexaploid: six sets of chromosomes, in three pairs of ancestries called A, B and D. Each set came from a different wild grass. An early hybridisation joined two of them into the tetraploid wheats, the pasta wheats among them. A later hybridisation, with a goatgrass, added the D genome and produced the plant that mills into bread flour. The genomes were not blended into one. They sit alongside each other, all still in use. A 2014 reconstruction of the hybridisations put dates on the meetings. The order and the dates have been argued. The three-ness has not.

The D genome is a large part of why bread dough stretches. Gluten is a collaboration among genes that arrived on different days, from different species, and were never reduced back to a single copy. When you knead a loaf you are working a merger. The merger is also why wheat is both tough and genetically narrow in places: a plant with three genomes has a great deal of backup, and a great deal that has to be kept in step.