| Physical maps of chromosomes 6A, 6B and 6D and a consensus physical map of the group-6 chromosomes of common wheat were constructed using 128 DNA clones and 45 group-6 deletion lines. Of the 50 segments defined by the 45 deletion lines, 36 are tagged by molecular markers. Among the 128 clones, 45 detected 3 loci, 35 detected 2 loci and 38 detected 1 locus. Seventy, 90 and 92 loci were mapped in 6A, 6B and 6D respectively. Except for one probable short arm inversion, the linear order of loci among the three chromosomes is almost identical. Eighty-three loci were placed on the group-6 consensus physical map.; The group-6 consensus physical map was compared with 11 linkage maps of homoeologous group-6 chromosomes from 6 Triticeae species as well as rice. Based on the comparison, a consensus physical map of Triticeae group-6 chromosomes composed of 86 markers was constructed. The order of loci is largely conserved on both the linkage and physical maps among these species. Although colinearity was observed for 220 of 233 comparisons, the relative distribution of loci on the physical and linkage maps differs markedly. On all three of the physical maps, 90 percent of the loci are located in the distal halves of the arms, and most loci are in 2 or 3 clusters. In contrast, on the linkage maps, most loci are either distributed relatively evenly or clustered around the centromere. This difference is the result of differential rates of recombination over the length of chromosomes, with a higher rate in the terminal regions and a lower rate in the proximal regions of the chromosome arms.; Evidence from this study suggests that the order of two 6AL deletions, 6AL-2 and 6AL-8, should be reversed and that chromosome 6B differs from 6A and 6D by a short inversion. |
