Figure 3.

Major mutations and morphological changes during wheat domestication. 1, The transition from ssp. dicoccoides to ssp. dicoccon involved mutation in the Brittle rachis loci. Some modern emmer wheat lines might also contain mutations in some but not all loci affecting free threshing. 2, Free-threshing tetraploid wheat, named ssp. parvicoccum, appears in the archeological record approximately 2,000 years before ssp. durum. It is now extinct but might have resembled the tetraploid wheat (Genome BBAA) shown here as ssp. X that was extracted from hexaploid wheat and has a compact spike and small grains. Its genotype must have been similar to durum, namely free threshing with soft glumes, with mutants Q and tg-A1, tg-B1. 3, The hybridization of this free-threshing tetraploid wheat with the DD subgenome donor, Ae. tauschii, gave rise to a primitive hulled hexaploid wheat, different from spelt wheat due to the Q factor, and absent from the archaeological record. It likely resembled the picture shown from a synthetic hexaploid between ssp. durum and Ae. tauschii shown here. 4, Soon after its formation, hexaploid wheat became free threshing thanks to a mutation in Tg-D1 and its rachis became thicker thanks to a mutation in Br-D2.