A CYTOGENETIC LADDER-MAP OF THE WHEAT HOMOEOLOGOUS GROUP-4 CHROMOSOMES

We report the results of chromosome maps of wheat homoeologous chromos omes 4A, 4B, and 4D using 40 RFLP markers and 39 homozygous deletion l ines. Deletion breakpoints divide the chromosomes into 45 sub-arm inte rvals with 32 intervals distinguished by molecular markers. The chromo some maps confirm the homoeology of arms 4AS to 4BL and 4DL, and 4AL t o 4BS and 4DS. The chromosome map of 4A reveals novel information conc erning the 4AL-5AL-7BS cyclical translocation. The presence of homoeol ogous group-4 long-arm markers, Xksu C10 and Xpsr 1051, intervening be tween the translocated 5AL and 7BS chromosome segments in 4AL suggests that the translocation events are more complex than was earlier belie ved. Chromosome maps confirm a pericentric inversion in Chinese Spring chromosome 4B. The consensus chromosome map is compared to the geneti c map of wheat to construct a cytogenetic ladder-map (CLM). The CLM re veals an unequal distribution of recombination along the length of the chromosome arms. Recombination is highest in the distal half, and low in the proximal half, of the chromosome arms.