IV. 4. Coordinator's Report: Chromosome 3.
Ryuhei Takahashi, Institute for Agricultural and Biological Sciences, Okayama University, Kurashiki, Japan.
Søgaard (1971, 1973) reported that several genes, zb, ert-c, cer-r, uz, cer-zd and cer-zn were arranged in this order on chromosome 3, and she made four three-point tests to reconfirm the previous results in 1976. As seen in Fig. 1, the result differed from the previous one, indicating that the gene order was cer-zd, ert-c, uz, cer-r and cer-zn.
Fig. 1. Map of five genes located by Søgaard (1976).
Linde-Laursen (1982) made an interesting experiment using an indigenous device which allowed him to compare "cytological" positions of three c-band locations (1, 2, and 3) on the long arm of chromosome 3, and further to locate these three band locations relative to three markers, cer-zd, uz and cer-zn, on the linkage map of the same chromosome. Results are shown in Fig. 2. These indicate that, whereas three C bands are considerably apart from each other on the cytological map, no recombination is observed between C bands (1) and (2), and only 12% recombination is found between (2) and (3), which suggest that recombination is virtually confined to the distal half of this chromosome arm. The three markers are located rather closely to the centromere in the order of cer-zd, uz and cer-zn.
Eslick and McProud (1974) have located a gene for male sterility, msg-5, between al and ert-c on chromosome 3 (Fig. 3), and inferred that the gene msg-5 and most probably ert-c are very near to centromere.
Fig. 3. A map of five genes on chromosome 3 by Eslick and McProud (1974).
The results presented above suggest to us that the seven genes, al, msg-5, cer-zd, ert-c, uz, cer-r and cer-zn are rather closely linked and probably arranged in this order, and further that the centromere of chromosome 3 is located within this chromosomal region. Singh and Tsuchiya (1974) have suggested that the centromere is located between yst and zb, and according to Kasha and Walker (1960), the distance between ys and uz (very close to zb) is only 4%. However, on account of some discrepancies among the estimated distances between these genes, it is hard to determine the order of these genes and which of them are truly located on the short or long arm of chromosome 3. Further genetic and cytogenetic analyses are needed to solve these problems.
Takahashi et al. (1974) and Moriya and Takahashi (1974, 1980) determined the locations of cu-2 (curly-2), sca (short and crooked awn) and wst,,j (white stripe) by means of three point tests. Konishi (1970, 1975 and unpublished) studied the linkage of two dwarf genes, lzd and sld, in relation to several genes known to be on this chromosome using multiple tester stock. In these experiments all the linkage data were obtained by F2 and F3 progeny tests from which the weighted average values of recombination were calculated. Fig. 4 presents five linkage maps separately obtained in the above experiments, and also a chromosome map finally set up from these five maps. Konishi estimated a linkage map after the procedure developed by J. Jensen and J. Helms Jørgensen (1975), using the genetic data ln these experiments, and found that the gene order shown in Table 4 proved to be quite valid.
Singh et al. (1982) reported that a telotrisomic chromosome previously designated as 3A was truly the long arm (3L). Moreover, they obtained a new telotrisomic for 3S and studied F2 segregation from crosses between 3S and three markers, uz, al and ac. The results have indicated that al is associated with 3S but uz is on the long arm. However, the gene ac, which has been known to be close to al, does not associate with 3S, and hence it is recognized to be on long arm or the 3S used in this experiment is deficient for the segment carrying ac.
With respect to the order of the genes uz and cu-2, Tsuchiya and Singh (1974, 1982) opined that cu-2 should be closer to the centromere than uz based on the fact that cu-2 plants appeared more than uz plants (18 vs. 10) among 158 disomic plants in F2 of a cross between triplo 3L (previously 3S) and a double recessive stock for uz and cu-2. Probably for this reason they changed the positions of uz and cu-2 on chromosome 3 (Tsuchiya 1982). However, their opinion can hardly be agreed with because of insufficient genetic evidence to support it. In my opinion it is most probable that uz is rather closer to the centromere than cu-2 as was shown by many authors in this report.
Finally a current linkage map of chromosome 3 is shown in Fig. 5 although relative positons of some gene loci, especially those which are very closely linked with each other, are not always trustworthy.
Fig. 5. Current linkage map of chromosome 3 prepared by Takahashi.
References:
Eslick, R. F. and W. L. McProud. 1974. Positioning of male sterile 5 (msg5) on chromosome 3. BGN 4:16-23.
Jensen, J. and J. Helms Jørgensen. 1975. The barley chromosome 5 linkage map. I. Literature survey and map estimation procedure. Hereditas 80 (reprint).
Kasha, K. J. and G.W.R. Walker. 1960. Several recent barley mutants and their linkages. Can. J. Genet. Cytol. 2:397-415.
Konishi, T. 1970. Studies on EMS-induced mutation in barley III. Nogaku Kenkyu 53:141-152 (in Japanese).
Konishi, T. 1975. Characteristics and inheritance of EMS-induced mutants in barley. Nogaku Kenkyu 55:53-56 (in Japanese).
Linde-Laursen, I. 1980. Segregation and linkage of genes on barley chromosome 3 in one cross combination tested by chromosome-doubled monoploids and by F2-data. BGN 10:42-44.
Linde-Laursen, I. 1982. Linkage map of the long arm of barley chromosome 3 using C bands and marker genes. Hereditas 49:27-35.
Moriya, I. and R. Takahashi. 1980. Linkage studies of three barley mutants. BGN 10:47-51.
Singh, R. J. and T. Tsuchiya. 1974. Further information on telotrisomic analysis in barley. BGN 4:66-69.
Singh, R. J., A. Shahla and T. Tsuchiya. 1982. Telotrisomic analysis of three newly obtained telotrisomic, triplo 3S, in barley. BGN 12:42-44.
Søgaard, B. 1971. Linkage studies on eceriferum mutants in barley. BGN 1:41-47.
Søgaard, B. 1973. Continued linkage studies on eceriferum mutants in barley. BGN 3:57-61.
Søgaard, B. 1976. Three point tests on barley chromosome 3. BGN 6:65-67.
Takahashi, R., J. Hayashi and I. Moriya. 1974. New linkage data obtained during 1972-73 season. BGN 4:74-76.
Tsuchiya, T. 1982. Linkage maps of barley. BGN 12:100-104.
Tsuchiya, T. and R. J. Singh. 1982. Chromosome mapping in barley by means of telotrisomic analysis. Theor. Appl. Genet. 61:201-208.
