The gene linkage map of chromosome 4 is given in Fig. 1. The map is unchanged from that presented in BGN 22 apart from the addition of the Height QTL (Hackett et al, 1992). There are 28 genes on the map covering a genetic distance of 136 cM. Thee centromere is unmapped and the cer-j locus has been assigned the 0 position. The short (S) and long (L) arms have been reversed from that presented in the 1990 BGN (Vol. 20) to reflect homoeology with other Triticeae group 4 chromosomes. The number of genes on the map represents only half of the genes known to be located on chromosome 4, and the lack of intrachromosomal mapping reflects a lack of polymorphism in current barley mapping populations. Molecular mapping of barley chromosome 4 with RFLP and PCR-based markers has been relatively slow. Tbe number of molecular markers on chromosome 4 is generally low compared with other barley chromosomes (Heun et al, 1991; Graner et al, 1991) and in some mapping projects no molecular markers have been assigned to this chromosome (Powell et al, 1992).
Graner, A., Jahoor, A., Schondelmaier, J., Siedler, H., Pillen, K., Fischbeck, G., Wenzel, G. and Herr-man, R.G. (1991). Construction of an RFLP map of barley. Aeor. Appl. Genet. 83, 250-256.
Hackett, CA., Ellis, R.P., Forster, B.P., McNicol, JW. and Macaulay, M. (1992). Statistical analysis of a linkage. experiment in barley involving quantitative trait loci for height and caremergence time and two genetic markers on chromosome 4. 77teor. Appl. Genet. 85, 120126.
Heun, M., Kennedy, A.E., Anderson, JA., Lapitan, N.L.V., Sorrells, M.E. and Tanksley, S.D. (1991). Construction of a restriction fragment length polymorphism map for barley (Hordeum vulgare). Genome 34, 437-447.
Powell, W., Barua, U.M., Chalmers, K.J., Thomas, W.T.B., Hackett, CA., Forster, B.P. and Waugh, R. (1992). A foundation linkage map of barley (Hordeum vulgare L.) with particular reference to developmentally important genes. Annual Report of the Scottish Crop Research Institute 1992, 31-33.