| In hexaploid dinkel wheats (AABBDD), many translocations were identified
by using monosomic or other aneuploid series of T. aestivum cv. Chinese
Spring (for a review, see Kawahara 1984). Chromosomes of the B genome are
most frequently involved in translocations followed by those of the D genome
and of the A genome. This tendency has become more apparent with the change
of the designation of 4A to 4B according to Dvorak (1983). Based on available data, the relative frequency of breakpoints on each genome was calculated as shown in Fig.1. The number of breakpoints on modified genomes, B, G and Sv, is clearly about twice that on the pivotal ones, A and Cu, in tetraploid species. Similarly, breakpoints are located mainly on the B genome chromosomes in hexaploid dinkel wheats as mentioned above. Therefore, it is concluded that genome rearrangement occurs more frequently in the modified genomes than in the pivotal ones, and that the modified genomes probably evolved through their high structural variability rather than through introgression between different genomes. References DVORAK, J. 1983. The origin of wheat chromosomes 4A and 4B and their genome reallocation. Can. J. Genet. Cytol. 25: 210-214. KAWAHARA, T. 1984. Studies on intraspecific structural differentiation of chromosomes in the wild tetraploid wheats. Dr. thesis, Kyoto University, Kyoto. KAWAHARA, T. & TANAKA, M. 1983. Chromosomal interchanges and the evolution of the B and G genomes. Proc. 6th Int. Wheat Genet. Symp., Kyoto: 977-981. KIHARA, H. 1949. Genomanalyse bei Triticum und Aegilops. IX. Systematischer Aufbau der Gattung Aegilops auf Genomanalytischer Grundlage. Cytologia 14: 135-144. ZOHARY, D. & FELDMAN, M. 1962. Hybridization between amphidiploids and the evolution of polyploids in the wheat (Aegilops-Triticum) group. Evolution 16: 44-61. |
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