Towards an integration of the physical and the genetic chromosome maps of barley by in situ hybridization

The relationship between physical and genetic distances on the barley chromosomes was studied by fluorescence in situ hybridization (FISH). Physical mapping of low‐ and single copy genes by FISH includes the protein Zx gene on chromosome 4 (4I), the α‐amylase, high PI, genes on chromosome 6 (6I), the early‐methionine‐labelled polypeptide gene(s) on chromosome 5 (1I), and the leaf thionin genes on chromosome 6 (6I). Two interstitial sites of the telomere‐associated sequence, the HvRT‐family, were mapped by FISH on chromosome 3 (3I), and hybridization sites of histone 4 and ubiquitin genes were detected on chromosomes 1 (7I) and 5 (1I), respectively. In addition, a 5SrDNA locus was mapped genetically on chromosome 1. The study provides seven new anchor sites for integrating the genetic and physical chromosome maps and allows estimation of the relationship between physical and genetic distances to 1‐2 Mb/cM for the distal 40 % of the chromosome arms. All chromosome arms studied showed a strongly reduced level of recombination in their inner halves. These results are discussed in relation to the feasibility of map‐based cloning in barley and other cereal species.