IDENTIFICATION AND HIGH-DENSITY MAPPING OF GENE-RICH REGIONS IN CHROMOSOME GROUP-5 OF WHEAT

The distribution of genes and recombination in the wheat genome was st udied by comparing physical maps with the genetic linkage maps. The ph ysical maps were generated by mapping 80 DNA and two phenotypic marker s on an array of 65 deletion lines for homoeologous group 5 chromosome s. The genetic maps were constructed for chromosome 5B in wheat and 5D in Triticum tauschii. No marker mapped in the proximal 20% chromosome region surrounding the centromere. More than 60% of the long arm mark ers were present in three major clusters that physically encompassed < 18% of the arm. Because 48% of the markers were cDNA clones and the di stributions of the CDNA and genomic clones were similar, the marker di stribution may represent the distribution of genes. The gene clusters were identified and allocated to very small chromosome regions because of a higher number of deletions in their surrounding regions. The rec ombination was suppressed in the centromeric regions and mainly occurr ed in the gene-rich regions. The bp/cM estimates varied from 118 kb fo r gene-rich regions to 22 Mb for gene-poor regions. The wheat genes pr esent in these clusters are, therefore, amenable to molecular manipula tions parallel to the plants with smaller genomes like rice.