Chromosome structure of Triticum timopheevii relative to T-turgidum

The chromosome structure of four different wild populations and a cultivate d line of Triticum timopheevii (2n = 28, A(t)A(t)GG) relative to Triticum t urgidum (2n = 28, AABB) was studied, using genomic in situ hybridisation (G ISH) and C-banding analysis of meiotic configurations in interspecific hybr ids. Two wild accessions and the cultivated line showed the standard C-band ing karyotype. The other two accessions are homozygous for translocation 5A (t)/3G and translocations 1G/2G and 5G/6G. GISH analysis revealed that all the T. timopheevii accessions carry intergenome translocations 6A(t)/1G and 1G/4G and identified the position of the breakpoint in translocation 5A(t) /3G. C-banding analysis of pairing at metaphase I in the hybrids with T. tu rgidum provides evidence that four species-specific translocations (6A(t)S/ 1GS, 1GS/4GS, 4GS/4A(t)L, and 4A(t)L/3A(t)L) exist in T. timopheevii, and t hat T. timopheevii and T. turgidum differ in the pericentric inversion of c hromosome 4A. Bridge plus acentric fragment configurations involving 4AL an d 4A(t)L were identified in cells at anaphase I. This result suggests that the paracentric inversion of 4AL from T. turgidum does not exist in T. timo pheevii. Both tetraploid species have undergone independent and distinct ev olutionary chromosomal rearrangements. The position, intercalary or subdist al, of the breakpoints in species-specific translocations and inversions co ntrasts with the position, at or close to the centromere, of intraspecific translocations. Different mechanisms for intraspecific and species-specific chromosome rearrangements are suggested.