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Gene evolution
- From Crop Domestication to Super-domestication

Genome sequencing has enabled the evolution of domestication-relatedgenes to be elucidated. The wild and domesticated wheat speciesprovide an example. The different domesticated wheat cultigens(cultivated species) evolved from hybridization events betweenwild and cultivated species (to form Triticum aestivum subsp.spelta) or selections from either wild (T. monococcum subsp.monococcum and T. turgidum subsp. dicoccum) or domesticatedspecies (T. aestivum and T. turgidum subsp. durum). In thiswild–domesticated polyploid series the grain-hardnesslocus (Ha) of wheat encodes friabilins that are composed ofthree proteins. The genes Pina, Pinb and Gsp-1 at the Ha locusencode these three proteins. Two of these genes, Pina and Pinb,were eliminated from both the A and B genomes of wheat afterpolyploidization into the tetraploid T. turgidum. In the hexaploid,T. aestivum, Pina and Pinb are present coming from the D genomedonor, Aegilops tauschii. Comparison of the Ha locus in thesame genome in diploid, tetraploid and hexaploid Triticum andAegilops species revealed numerous genomic rearrangements, suchas transposable element insertions, genomic deletions, duplicationsand inversions (Chantret et al., 2005). Genomic rearrangementsat the Ha locus were believed to be mainly caused by illegitimaterecombination, where DNA sequences not originally attached toone another become joined, and this type of recombination isconsidered a major evolutionary mechanism in wheat species (Chantret et al. 2005).The complex evolution of the Ha locus in wheat reflects theremarkably high rate of DNA replacement in wheat genes (Dubcovsky and Dvorak, 2007).

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