IV.6. Coordinator's Report. Chromosome 5.

Jens Jensen. Agricultural Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark.

The inhibitors of both chymotrypsin and microbial serine proteases, CI-1 and CI-2, which are present in barley kernels, could not be detected in kernels from the set of wheat addition lines by Hejgaard and Bjørn (1983). They suggest that the two proteins are coded for by the long arm of chromosome 5 as the addition lines do not comprise that chromosome arm. Furthermore, they propose Ica1 and Ica2 as locus designations for the inhibitors (inhibitor of chymotrypsin Aspergillus protease CI-1 and CI-2, respectively).

Two mutants with high thousand-grain weight and with gigas morphology designated (Gig) were incompletely dominantly inherited. Both mutant genes were located to chromosome 5 by translocations. The gene is one of the mutants (Dbg 633) gave recombination frequencies with the powdery mildew resistance gene Ml-a of 47.64 + 8.40 and 42.5 + 7.82 (the standard deviation corrected by the coordinator) (Schriber 1982).

In order to map Hor3, Shewry et al. (1983) obtained a number of recombination percentages in three crosses. The recombination percentages are given in Table 1.

Table l. Linkage data affecting the 1984 map. Only recombination percentages underlined are considered. Those marked with an asterisk did not fit and are omitted.

A linkage map of chromosome 5 (Fig. 1) was estimated by the procedure described by Jensen and Jørgensen (1975a, b). Table 1 summarizes the new recombination percentages added relative to those in last year's report. It also gives the previously accepted recombination percentages that have been excluded from the map estimation because they do not fit the map comprising the new data. The last column in Table l shows the corresponding map estimates in recombination per cent.

Fig. 1. The barley chromosome 5 linkage map width the best fit to all available linkage data. The map positions are given in centimorgans (cM). The order and positions of some M1- loci and of closely linked loci may be indefinite. The position of the centromere is probably slightly above that of fs2.

Before utilizing new linkage data in the mapping procedure, I normally - if it is possible - check the recombination percentages and the standard deviations. In the paper by Shewry et al. (1983) the standard deviations of the higher recombination frequencies deviate in some cases from my checks possibly due to rounding errors. In spite of this, the author's standard deviations are given in Table 1. To illustrate the importance of avoiding rounding errors, let us assume that a simple rounding error gives a standard deviation of 0.8 instead of the correct value of 0.9. In such a case the recombination percentage will be given a weight correspoinding to a 25% larger experimental material.

Two major changes on the linkage map have occurred since last year: l) the Hor3 locus has moved from position 31 to position 8, and 2) the Hor1 and Hor2 loci have moved significantly relative to Ml-k and Ml-a in the direction of a lower map position.

The positions of Ml-at, Ra4, ml-d and Ml-nn are based on less reliable data. I have unpublished data showing that Ml-p is not located on chromosome 5.

References:

Blake, T. K., S. E. Ullrich, and R. A. Nilan. Mapping of the Hor3 locus encoding D hordein in barley. - Theor. and Appl. Genet. 63:367-371.

Doll, H. and A. H. D. Brown. 1979. Hordein variation in wild (Hordeum spontaneum) and cultivated (H. vulgare) barley. - Can. J. Genet. Cytol. 21:391-404.

Hejgaard, J. and S. Bjørn. 1983. Location to barley chromosomes of genes for some major grain protease inhibitors. - BGN 13:53-54.

Jensen, J. and J. H. Jørgensen, 1975a. The barley chromosome 5 linkage map. I. Literature survey and map estimation procedure. - Hereditas 80:5-16.

Jensen, J. and J. H. Jørgensen. 1975b. The barley chromosome 5 linkage map. II. Extension of the map with four loci. - Hereditas 80:17-26.

Jensen, J., J. H. Jørgensen, H. P. Jensen, H. Giese, and H. Doll. Linkage of the hordein loci Horl and Hor2 with the powdery mildew resistance loci Ml-k and Ml-a on barley chromosome 5. - Theor. App. Genet. 58:27-31.

Schreiber, H. 1982. Lokalisierung von Korngrose-Genen mit Hilfe von Translokationen bei Gerste (Hordeum vulgare L.). - Arch. Zuchtungsforschung, Berlin 12:173-182.

Shewry, P. R., A. J. Faulks, P. A. Pickering, I. T. Jones, R. A. Finch, and B. J. Miflin. 1980. The genetic analysis of barley storage proteins. Heredity 44:383-389.

Shewry, P. R., R. A. Finch, S. Parmar, J. Franklin, and B. J. Miflin. 1983. Chromosomal location of Hor3, a new locus governing storage proteins in barley. - Heredity 50:179-189.

BGN 14 toc
BGN Main Index