V.1. Linkage maps of barley as of March 1974.
T. Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, Colorado 80521, U.S.A.
The linkage maps published in BGN 3 (99-103), particularly the map for chromosome 3, have been criticized by R. Takahashi of Japan mainly based on his results from conventional linkage analysis with the marker gene uz and others (Takahashi, personal communication). Re-examination of various marker genes, not only genes in chromosome 3 but also other chromosomes, has been conducted using telotrisomic analysis (Singh and Tsuchiya, 1974). From these experiments it has been found that the arm location of yst2 and xc should be changed.
Other reports on linkage analysis include coordinator's report on some chromosomes. However, standard or established markers have not been used in some cases so that it has been difficult to find reliable location of some new genes in the map. Also it has been shown by telotrisomic analysis (Tsuchiya and Singh, 1973; Singh and Tsuchiya, 1974) that previous maps are not always reliable regarding the order of the genes in the map. It is, therefore, the present author's opinion that reliable linkage maps should be developed based on the information obtained from various cytogenetic methods including telotrisomic analysis.
The linkage maps are developed mainly based on the available information from recent reports including those in BGN Vol. 4. Many genes used in these linkage analyses could not be located in the linkage maps because (1) established or standard marker genes have not been included in the analysis, and (2) arm location of these genes has not been established by telotrisomic or other analysis.
A considerable amount of information has been obtained for linkage of various markers. Since no information is available for the arm location of these genes, it is difficult to locate them in the map. These genes for which chromosomal location has been established are listed under the map of each chromosome. The gene order in the maps may not be always correct since the linkage information so far reported is not considered to be reliable in some cases.
The centromere location was designated as C = in each map. For chromosome 5 it was shown by an arrow which indicates the direction in which the centromere should be located.
Detailed information for each chromosome is given below:
Chromosome 1.
No coordinator's report was received. However, Søgaard (1974)
reported on the results of three point tests using mostly new mutants.
Since only one previously established marker gene in the map has been included
in the analysis and arm location of these genes has not been established,
results could not be used for mapping. These genes are listed under the
map.
Chromosome 2.
Coordinator's report described various changes, but no map was provided
(Walker, 1974. BGN 4:99).
Allelism test showed that f for chlorina is allelic to lg for light green (Tsuchiya, 1974. BGN 4 :7 9 ). Since f has priority, lg was eliminated from the map. Telotrisomic analysis showed that sk and gs6 are located on the short arm (2S) (Singh and Tsuchiya, 1974) and listed under the map together with mt reported by Takahashi et al. (1974).
Chromosome 3.
Considerable change was required based on the additional information
from telotrisomic analysis (Singh and Tsuchiya, 1974. BGN 4 : 66 ). The
genes cu2, uz, and wst are all moved back to the short
arm.
Telotrisomic analysis also showed that xc (and maybe ac) should move from the short arm (3S) to long arm (3L). The genes zb for zebra, cer-zn348 for glossy spike (eceriferum) and gs2 for glossy sheath and spike were located on 3S (Singh and Tsuchiya, 1974).
Additional linkage data for some genes (Eslick and McProud, 1974; Nonaka, 1974; Singh and Tsuchiya, 1974; Takahashi et al., 1974) made it difficult to delineate some old and new genes in the map. These genes are listed under the map for chromosome 3.
Centromere position was located between zb and yst.
Since the existing information on the gene order in the map is not reliable, the centromere position should be considered tentative. For detail refer to Singh and Tsuchiya (1974).
More extensive linkage analysis using various multiple marker stocks and trisomic stocks is necessary to develop reliable linkage map in this chromosome.
Chromosome 4.
The main accomplishment in the mapping of chromosome 4 is the location
of the centromere, and the arm location K locus which is one of
the important key markers in this chromosome (Singh and Tsuchiya, 1974).
The map prepared by the coordinator, T. E. Haus (BGN 4:101) was used here.
The gene cer-j for glossy seedling was found to be allelic to gl3 (Haus, 1974; Tsuchiya, unpublished data). The gene ari-c was also found to be allelic to lk5 (Tsuchiya, 1974), so that lk5 was used in this map instead of ari-c in Haus' map.
Chromosome 5.
The linkage map has been developed by the new coordinator, J. Jensen,
for this chromosome based on detailed analysis of available linkage data
(Jensen, 1974a,b,c). However, his treatment has some problems such as exclusion
of f7 for chlorina which is good marker stock, changing many gene
symbols, and deletion of gene (JMl-nz) based on simple assumption.
Also Jensen (1974c) changed the order of many genes without critical experiments using multiple marker stocks. Arm locations of many genes are not known yet. Consequently, some genes mapped by Jensen (1974c) were not located in this map. Also previous gene symbols were used in this map for the genes for powderly mildew resistance.
Chromosome 6.
No coordinator's report was received. A new gene, msg, ,bk,
for male sterility was located in this chromosome (Eslick and McProud,
1974) and listed under the map.
Chromosome 7.
Linkage data of several genes in this chromosome were presented by
Søgaard (1974). Most genes analyzed in her three point test (actually
F2 analysis) were new mutant genes and established markers have not been
included except va which is still questionable in its location in
the map. It is difficult, therefore, to locate these new genes in the map.
The map presented in this paper is almost the same as the one in 1973 (Tsuchiya,
1973). Most of the new genes analyzed by Søgaard (1974) are listed
under the map. For detailed information refer to Fedak (1974) and Søgaard
(1974).
It is obvious from this summary that the use of multiple genetic marker stocks is necessary in linkage analysis. The multiple marker stocks should include at least one good key marker which has been used extensively in the past.
Each coordinator is urged to start establishing various multiple marker stocks for the chromosome for which the coordinator is responsible.
FIG. 1. CHROMOSOME MAPS OF BARLEY
References:
1. Eslick, R. F., R. T. Ramage and D. R. Clark. 1974. BGN 4:11-15.
2. Eslick, R. F. and W. L. McProud. 1974. BGN 4:16-23.
3. Fedak, G. 1974. BGN 4:106-107.
4. Haus, T. E. 1974a. BGN 4:31-33.
5. Haus, T. E. 1974b. BGN 4:101-102.
6. Jensen, J. 1974a. BGN 4:40-42.
7. Jensen, J. 1974b. BGN 4:102-106.
8. Jensen, J. and J. H. Jørgensen. 1974. BGN 4:42-43
9. Jørgensen, J. H. 1974. BGN 4: 43-44.
10. Nonaka, S. 1974. BGN 4 56-58.
11. Singh, R. J. and T. Tsuchiya. 1974. BGN 4: 66-69
12. Søgaard, B. 1974. BGN 4: 70-73.
13. Takahashi, R.; J. Hayashi and I.Moriya. 1974. BGN 4: 74-76.
14. Tsuchiya, T. 1973. BGN 3: 99-103.
15. Tsuchiya, T. 1974. BGN 4:79.
16. Tsuchiya, T. and R. J. Singh. 1973. BGN 3: 75-78
17. Walker, G. W. R. 1974. BGN 4: 99-100.
The work reported in the paper V.1 (p. 126-130) was supported in part
by NSF Research Grant GB 30493 and CSU Experiment Station Project (Hatch
8).
