Physical mapping of the B-hordein loci on barley chromosome 5 by in situ hybridization

Physical mapping of the B-hordein genes in barley (Hordeum vulgare cv. Betzes) was achieved by in situ hybridization of a biotin-labelled B-hordein cRNA probe to chromosome spreads. Lines trisomic for chromosome 5 showed up to 3 signals on interphase nuclei, while no more than 2 signals were observed in normal diploids. An enzyme pretreatment, which produced broken cells, increased the frequency of signal detection. A clear signal was observed on 23% of interphase nuclei and 0.025% of metaphase spreads. The B-hordein genes mapped to 46% of the distance from the centromere on the short arm of chromosome 5. These results are discussed in relation to the barley genetic map and to previous reports of in situ hybridization of low-copy and unique-copy genes in plants.Key words: in situ hybridization, Hordeum vulgare, B-hordein genes, genetic map.