II. 31 Trisomic analysis of lg4 and zbc.
Lindy Seip and T. Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
*Partly supported by research grant from U.S. Department of Agriculture (12-14-5001-265) as a cooperative project with Colorado State University.
1. Analysis of lg4: The gene lgI for chlorina or light green was first reported by Immer and Henderson (1943). Later Robertson et al. (1947) assigned the symbol lg4 for lgI and also lg9 which is allelic to lgI. The gene lg4 was located on chromosome 4 with the following repulsion cross-over values:
The average values of the combined percentage recombinations of repulsion and coupling are as follows (Immer and Henderson, 1943):
Tsuchiya and Haines (1975) studied the chromosomal association of lg4 by means of primary trisomic analysis. The segregation ratio for +: lg4 was 67:11(N=78) which deviated from Mendelian ratio of 3:1 (x2=4.940). This result suggests the trisomic ratio. Also, the chromosome numbers of 11 recessive homozygotes were all 2n=14, suggesting a trisomic ratio. Since the number of plants in the F2 population was rather small and the chromosome numbers of all plants were not studied, the results were not conclusive regarding the chromosomal association of lg4.
This report deals with trisomic analysis to further study the chromosomal association of lg4. The primary trisomic for chromosome 4 (Robust or Triplo 4) was crossed with lg4 homozygote. The trisomic F1 plant was selfed to obtain the F2 seeds (Tsuchiya, unpublished) which were used in this experiment. Chromosome numbers were counted in all plants and the segregation ratios were recorded. The results was summarized in Table 1.
The results for diploid control fit the 3:1 ratio. The segregation in the 2x portion of F2 Triplo 4 x lg4 also fits to 3:1 possibly due to an insufficient population size and poor germination rate; only 74 out of 106 seeds germinated and survived. No 2x + 1 plant was lg4 homozygote as in the previous experiment by Tsuchiya and Haines (1975). The value for the total does not fit to the 3:1 ratio nor to fit the trisomic ratio for 25% transmission; 11:1.
Combining the current data with the 1975 result, the results seem to suggest the trisomic ratio. The lack of homozygous recessive plants in the trisomic portion support the association of lg4 with chromosome 4, although more data is necessary to draw definite conclusions on the chromosomal association of this gene, lg4.
2. Analysis of zbc: The chromosomal association of the gene zbc for zebra Colorado have been a controversial one. The linkage relations between zbc and some markers on chromosome 4 are as follows (cf. Tsuchiya, 1974:
Even though the information given above suggests the association of zbc with chromosome 4, there are some problems to be solved. First the genetic stocks used by several workers may not have been the same (Tsychiya, 1975). An experiment with primary trisomic analysis suggested that the gene zbc was not on chromosome 4 (Sinha, 1967; Tsuchiya, 1969). Further experiments of the gene zbc in the CSU stock B 8-9 by means of primary trisomic analysis with Triplo 4 (Robust) showed a disomic ratio (Tsuchiya, 1974; Tsuchiya and Haines, 1975). In order to obtain additional information the trisomic analysis was conducted again in the cross between Triplo 4 and zbc (CSU B 8-9) with the results shown in Table 2 which also included the previous results reported by Tsuchiya (1974).
The results shown in Table 2 indicate that the gene zbc in the CSU stock B 8-9 is not located on chromosome 4, since (1) an appreciable number of recessive homozygotes (5 out of 40) were trisomic plants, and (2) the data fit to 3:1 ratio in both 2x and 2x + 1 portions in the 1977 experiment, although the segregation ratio in the sum of 2x and 2x + 1 did not fit to 3:1 ratio. Detailed trisomic analysis using all seven trisomic lines and several zbc stocks is now in the progress.
References:
Immer, F.R. and M.T. Henderson. 1943. Linkage studies in barley. Genetics 28:431.
Robertson, D.W., G.A. Wiebe and R.G. Shands. 1947. Summary of linkage studies in barley: Supplement I, 1940-1946. J. Amer. Soc. Agron. 39:464-473.
Sinha, R.P. 1967. Recombinagenic effect of certain chemicals applied to the genus Hordeum. Ph.D. Thesis, Univ. Manitoga, Winnipeg, Manitoba.
Tsuchiya, T. 1969. Status of studies of primary trisomics and other aneuploids in barley. Genetica 40:216-232.
-----. 1974. Report from Genetic Stock Center at Fort Collins, Colorado, BGN 4:107-110.
-----. 1975. Allelic relationships of some morphological and chlorophyll mutants in barley. BGN 5:64-67.
----- and R. Haines. 1975. Trisomic analysis of nine mutant genes in barley. BGN 5:67-69.
