Figure 8.29: Modern bread wheat, Triticum aestivum, is a hexaploid with genes derived from three different species. Two diploid species, T. uratu (n = 14) and probably Aegilops speltoides or a related species (n = 14), originally crossed to produce a diploid hybrid (2n = 14) that underwent chromosome doubling to create T. turgidum (4n = 28). A cross between T. turgidum and A. tauschii (2n = 14) produced a triploid hybrid (3n = 21) that then underwent chromosome doubling to eventually produce T. aestivum, which is a hexaploid (6n = 42).