An improved translocation tester-set for use to localize barley genes has been proposed based on karyotype analyses of 61 reciprocal translocations (Marthe and Künzel 1994). For barley chromosome 6 it includes, in addition to the translocations proposed by Linde-Laursen (1988), T4-5ai and T2-5ah with breakpoints on respectively the plus and the minus arm of chromosome 5.

By the important technic for physical mapping of the chromosomes, in situ hybridization, a site named Nor-I1 is localized to the plus arm of barley chromosome 5 based on a wheat ribosomal clone pTA71 containing the 18S-5.8S-26S rRNA gene (Leitch and Heslop-Harrison 1992). The location of Nor-I1 has been verified by Pedersen and Linde-Laursen (1994). They reported the site to be located at position +20 mGN (milligenomes ( cf. Jensen and Linde-Laursen (1992)).

A combined physical and genetical mapping was done using four probes developed from the short chromosome arm (plus arm) of barley chromosome 5 by microdissection of the arm from the ditelocentric line telo-5S. The four probes were mapped to five sites on chromosome 5 together with other molecular markers in progeny from the cross 'Vada' x 'Hordeum spontaneum' (Schondelmaier et al. 1993). The sites are probably located on the plus arm of chromosome 5. Unfortunately, only a linkage map of chromosome 5 with distances without standard deviations was given. Therefore, the linkage information can not be utilized to estimate the linkage map shown in Figure 1, and the preciseness of the map positions cannot be evaluated. The distance on their map locates a site 37.6 cM proximal to locus Hor1. Considering Figure 1 below suggests that position +24.5 is located on the plus arm of chromosome 5 close to locus Ndh5. Since it previously hase been indicated that the centromere is located above locus fs2 then the best estimate of the centromere position is in the region +17.4 to +24.5 cM.

In an experiment conducted to study recombination in the Mla barley powdery mildew resistance locus using the hordein loci Hor1 and Hor2 as flanking markers, the following order of the loci Hor1, Mla6, Mla13, Mla14, Hor2 was found and the distances for Hor1-Mla6, Mla6-Mla13 and Mla13-Hor2 were reported to be 3.9, 0.2, and 5.2 cM, respectively (Mahadevappa et.al. 1994). Further, in the same material RFLP markers were localized inside the Hor1-Hor2 region of chromosome 5 (DeScenzo et.al. 1994). Unfortunately no standard deviations are given in either of the publications so that the linkage information can not be used to improve the current linkage map (Figure 1).

Additional estimates of the distances between loci Hor1, Hor2 and Mla12 were given by Liu et al. (1994). Molecular and biochemical markers were applied on chromosome-doubled haploid lines from a cross of a winter with a spring barley to establish a linkage map of the seven barley chromosomes. A QTL for heading date was found associated with markers on chromosome 5 (Pan et al. 1994). More markers are added to the previously published map based on the winter barley cross 'Igri' with 'Franka' (Graner et.al. 1994). Based on chromosome-doubled haploids from the cross 'Harrington' x 'TR306' a linkage map was presented (Kasha et al. 1994) and quantitative trait loci were associated with the chromosome markers (Tinker et al. 1994). An update of the previously published map based on the 'Steptoe' x 'Morex' cross is given by Kleinhofs et al. (1993,1994), and a summary of QTL effects in the cross is given by Hayes et al. (1994). A linkage map of the seven barley chromosomes including morphological, biochemical, RFLP and RAPD markers was presented by Giese et al. (1994). The map was based on chromosome-doubled haploids from the cross 'Alf' x 'Vogelsanger Gold'. All the above reports have not given recombination percentages with standard deviations between the individual loci. Therefore, the linkage information can not be used in improving the linkage map shown in Figure 1.

The individual marker scoring of the individual progeny line, if not published, may be available in different forms from the internet or from the author. However, there is no tradition for the coordinator to collect the raw data from electronic databases or that he requests them from other places, nor for authors to supply the coordinator with these data. One consequence is that the linkage maps presented by the chromosome coordinators in BGN are incomplete.

In one report, Jin et al. (1993) gave recombination percentages with standard deviations as well as segregation data. However, the only case of chromosome 5 markers studied were trd and nec1. A chi-square was calculated to test if they were linked. Due to limited progeny size (although not small) the chi-square was not significant (a chi-square of 3.84 was apparently used as significance limit) and for that reason the author has probably not calculated the recombination percentage and its standard deviation. However, according to the distance between trd and nec1 in Figure 1, it is unlikely that a significant chi-square should be obtained. If it had occurred it had to be by chance and in such a case the recombination percent would have been lower than 44.5, which corresponds to the distance between trd and nec1 in Figure 1. Such results should have been reported and could have been included for estimating the map in Figure 1. In order not to bias the map, large distances showing insignificant linkage should also be considered in map estimation. From the report of Jin et al. (1993) the coordinator has calculated the recombination percent between trd and nec1 to be 45.785 ± 3.187.

Based on this value, on linkage information in former issues of BGN and using the procedure by Jensen (1987), the linkage map of barley chromosome 5 was estimated. A drawing of the map is shown in Figure 1. The map includes indication of the position of the centromere. The proximal value is based on the data by Schondelmaier et al. (1993). It may be erroneous, but it is the most likely position yet. The distal value is a minimum value.

The reports by Graner et al. (1993) and Kleinhofs et al. (1993) indicate the position of the centromere on chromosome 5, but they give no documentation for how it was obtained. However, the position suggested by Graner et al. (1993) compares well with the one given in Figure 1.

References:

DeScenzo, R.A., Wise, R.P. and M. Mahadevappa. 1994: High-resolution mapping of Hor2/Mla/Hor2 region on chromosome 5S in barley. Molecular Plant-Microbe Interactions 7:657-665.

Jin, Y., Franckowiak, J.D. and G.D. Statler. 1993: Linkage among some of the morphological markers in Wolfe's stocks. BGN 22:25-26.

Giese, H., Holm-Jensen, A.G., Mathiassen, H., Kj`r, B., Rasmussen, S.K., Bay, H. and J. Jensen. 1994: Distribution of RAPD markers on a linkage map of barley. Hereditas 120:267-273.

Graner, A., Bauer, E., Kellermann, A., Kirchner, S., Muraya, J.K., Jahoor, A. and G. Wenzel. 1994: Progress of RFLP-map construction in winter barley. BGN 23:53-59.

Hayes, P.M., Iyamabo, O. and the North American Barley Genome Mapping Project. 1994: Summary of QTL effects in the Steptoe x Morex population. BGN 23:98-143.

Jensen, J. 1987: Linkage map of barley chromosome 4. In: Barley Genetics V. Okayama, Japan:189 199.

Jensen, J. and I. Linde-Laursen. 1992: Statistical evaluation of length measurements on barley chromosomes with a proposal for a new nomenclature for symbols and positions of cytological markers. Hereditas 117:51-59.

Kasha,K.J., Kleinhofs, A. and the North American Barley Genome Mapping Project. 1994: Mapping of the barley cross Harrington x TR306. BGN 23:65-69.

Kleinhofs, A.,Ilian, A and D. Kudrna. 1993: The NABGMP mapping progress report, Spring 1993. BGN 22:27-41.

Kleinhofs, A.,Kilian, A.,Kudrna, D. and the North American Barley Genome Mapping Project. 1994: The NABGMP Steptoe x Morex mapping progress report. BGN 23:79-83.

Leitch, I.J. and J.S. Heslop-Harrison. 1992: Physical mapping of the 18S-5.8S-26S rRNA genes in barley by in situ hybridization. Genome 35:1013-1018.

Linde-Laursen, I. 1988: Gimsa C-banding of barley chromosomes. V. Localization of breakpoints in 70 reciprocal translocations. Hereditas 108:65-76.

Liu,C.J., Heun, M. and M.D.Gale. 1994: Intrachromal mapping of seven biochemical loci in barley, Hordeum vulgare. Theor. Appl. Genet. 87:94-96.

Mahadevappa, M.,DeScenzo, R.A. and R.P. Wise. 1994: Recombination of alleles conferring specific resistance to powdery mildew at the Mla locus in barley. Genome 37:460-468.

Marthe, F. and G. Künzel. 1994: Localization of translocation break points in somatic metaphase chromosomes of barley. Theor. Appl. Genet. 89:240-248.

Pan, A., Hayes, P.M., Chen, F., Chen, T.H.H., Blake, T, Wright, S., Karsai, I. and Z. Bed. 1994: Genetic analysis of the components of winterhardiness in barley (Hordeum vulgare L.). Theor. Appl. Genet. 89:900-910.

Pedersen, C. and I. Linde-Laursen. 1994: Chromosomal location of four minor rDNA loci and a marker microsatellite sequence in barley. Chromosome Research 2:65-71.

Schondelmaier, J., Martin, R., Jahoor, A., Houben, A., Graner, A., Koop. H.-U., Herrmann, R.G. and C. Jung.1993. Microdissection and microcloning of the barley (Hordeum vulgare L.) chromosome 1HS. Theor. Appl. Genet. 86:629-636.

Tinker, N.A., Mather, D.E. and the North American Barley Genome Mapping Project. 1994: Main effects of quantitative trait loci in the Harrington/TR306 to-row barley. BGN. 23:72-78.

Fig. 1. The barley chromosome 5 linkage map with the best fit to all linkage data available in the scientific literature calculated according to Jensen (1987). The map positions are given in centimorgans (cM). The order and positions of closely linked loci may not be definitive.

Editor's Note: After publication of BGN 24, the coordinator for chromosome 5 noted errors in this map. Please see the corrected version in GrainGenes.