Figure

Fig. 2.2. Late in the 20th century and beginning of 21st century, DNA clocking methods became available and were used to trace the timeline of the evolutionary history of wheat shown here and for many of the crop plants (see Table 2.1). The A, B and D diploid ancestors of wheat diverged from a common ancestor 3 MYA. The first speciation bottleneck occurred when tetraploid wheat species arose around 0.5 MYA. The second polyploidy speciation bottleneck occurred around 0.1 MYA when hexaploid wheat arose in a farmer’s field. The last bottleneck arose during wheat domestication when first farmers selected rare mutants at loci such as non-shattering (br, non-brittle rachis) and free-threshing (tg, the non-tough glume; and Q, the square spike) and others listed in Table 2.1. Source: Gill et al. (2014), fig. 1.