Sizing the genetic and physical centromere of barley chromosomes as a prerequisite of understanding genome evolution in the genus Hordeum

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Entire genome characterization of the important crop species barley requires knowledge of the correlation between the genetic and physical maps. Genetic map distances are based on recombination values and can not be linearly translated into actual physical distances of molecular markers or genes. In regions with suppressed recombination, i.e. the genetic centromeres and pericentromeric regions of barley chromosomes, genetic resolution is low and short genetic distances between markers may translate to long physical distances. Here the order of gene/marker loci can be resolved by physical or cytological mapping. In order to improve the resolution of the physical map of barley in the (peri)centromeric region of chromosome 3H we intend to use fluorescence in situ hybridization (FISH) to resolve the physical linear order of 100 repeat-free single-copy sequences, which were genetically assigned to a 10cM bin around the centromere. The sequence composition of the centromere will be determined based on FISH-anchored BACs. Furthermore, the established order of these probes on barley chromosome 3H will be used to test for their order in related Hordeum species and to evaluate the extent of chromosome rearrangements that might have played a role in the evolution of the genus Hordeum.