Saturation mapping of a gene-rich recombination hot spot region in wheat

Physical mapping of wheat chromosomes has revealed small chromosome segment s of high gene density and frequent recombination interspersed with relativ ely large: regions of low gene density and infrequent recombination. We con structed a detailed genetic and physical map of one highly recombinant regi on on the long aim of chromosome 5B. This distally located region accounts for 4% of the physical size of the long arm and at least 30% of the recombi nation along the entire chromosome. Multiple crossovers occurred within thi s region, and the degree of recombination is at least 11-fold greater than the genomic average. Characteristics of the region such as gene order and f requency of recombination appear to be conserved throughout the evolution o f the Triticeae. The region is more prone to chromosome breakage by gametoc idal gene action than gene-poor regions, and evidence for genomic instabili ty was implied by loss of gene collinearity for six loci among the homeolog ous regions. These data suggest that a unique level of chromatin organizati on exists within gene-rich recombination hot spots. The many agronomically important genes in this region should be accessible by positional cloning.