The linkage map given in Fig. 1 is based on that calculated by Jensen (1987). There has been little work on intrachromosome mapping on genes on chromosome 4 since Jensen's 1987 paper. The only new data I am aware of is from our own work linking Vrnl, Bmyl, and Wsp3 to the long arm on chromosome 4 (Forster and Ellis, 1991; Hackett et al., 1991). The vernalization gene Vrn1 is probably the spring habit gene sh described by Takahasi and Yasuda (1970) since both are located 4 cM from Bmyl; however, there is disagreement on the dominance relationship. Dominant Vrnl codes for reduced vernalization requirement, i.e. spring habit (Hackett et al., 1992), whereas dominant Sh is required for winter habit (Takahashi and Yasuda, 1970). Vrnl, Bmyl, and Wsp3 have not yet been formally mapped with respect to other loci on chromosomes 4, but statistical programs, similar to those of Jensen and Jørgensen (1975), are being set up in collaboration with the Scottish Agricultural Statistics Services and will be available for future additions to the map. The biochemical marker gene Wsp3 is currently the most distal gene on the long arm and extends the total map to 136 cM. The orientation of Bmyl and Wsp3 has been established by mapping to ml-o (Thomas et al., 1992).
In addition to single major gene loci, two quantitative trait loci for height and ear emergence time have been mapped to the long arm of chromosome 4 (Forster and Ellis, 1991; Hackett et al., 1992), but as yet there is no consensus on how these are to be treated with respect to the conventional map.
Two restriction fragment length polymorphism maps have been recently constructed in barley (Heun et. al., 1991; Graner et. al., 1991) which include maps for chromosome 4 and the reader is referred to these papers for further details.
Forster, B. P. and R. P. Ellis. 1991. Two biochemical markers for spring/winter habit. In: Barley Genetics VI Proc. Int. Barley Genet. Symp., Helsingborg, Sweden, pp. 101-103.
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.
Hackett, C.A., R. P. Ellis, B. P. Forster, J. W. McNicol, and M. Macaulay. 1992. Statistical analysis of a linkage experiment in barley involving quantitative trait loci for height and ear emergence time and two genetic markers on chromosome 4. Theor. Appl. Genet. (submitted).
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.
Jensen, J. 1987. Linkage map of barley chromosome 4. In: Barley Genetics V Proc. Int. Barley Genet. Symp., Okayama, Japan, pp. 189-199.
Jensen, J. and J. H. Jørgensen. 1975. The barley chromosome 5 linkage map. I. Literature survey and map estimation procedure. Hereditas 80:5-16.
Thomas, W. T. B., W. Powell, B. P. Forster, and J. S. Swanston. 1992. The effects of three linked major genes (ml-o, Bmyl and Wsp3) on quantitatively varying characters in barley. Ann. Appl. Biol. (In press).