The gene linkage map of chromosome 4 is given in Fig. 1; apart from some changes in gene symbols, this map is unchanged from that presented in BGN 21. There are 27 genes on the map covering a genetic distance of 136 cM. The centromere is unmapped and the cerj 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). The number of genes on the map represents only half of the genes known to be located on chromosome 4, the lack of intrachromosomal mapping reflects a lack of multiple point linkage data. Molecular mapping of barley chromosome 4 with RFLP and PCR based markers has also been relatively slow. The number of molecular markers on chromosome 4 is generally low compared with other barley chromosomes (Heun et al., 1991; Graner et al., 1991); in at least two mapping projects that I am aware of chromosome 4 has been the last of the seven barley chromosomes to be assigned a linkage group. In the work by Graner et al. (1991) only four RFLPs were placed on the chromosome 4 linkage map using data from an intraspecific cross. However, data from an interspecific cross (Hordeum vulgare cv. Vada × H. spontaneum) produced a map with 18 RFLP loci. It would appear that interspecific mapping populations currently being used in constructing barley genetic maps are low in polymorphism for chromosome 4.

References:

Graner, A., A. Jahoor, J. Schondelmaier, H. Siedler, K. Pillen, G. Fischbeck, G. Wenzel, and R. G. Herrman. 1991. Construction of an RFLP map of barley. Theor. Appl. Genet. 83:250-256.

Heun, M., A. E. Kennedy, J. A. Anderson, N. L. V. Lapitan, M. E. Sorrells, and S. D. Tanksley. 1991. Construction of a restriction fragment length polymorphism map for barley (Hordeum vulgare). Genome 34:437-447.