II. 53. Telotrisomic analysis of yst3 and i in barley.
T. Tsuchiya and An Hang. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
1. The gene yst3 for yellow streak 3
The gene yst3 is a spontaneous mutant gene found in the variety Lion (Singh and Tsuchiya, 1973). Primary trisomic analysis suggested that the gene yst3 was associated with chromosome 2 with the following results (Table 1) (Tsuchiya and Alanko, 1976):
Table 1. F2 data for primary trisomic analysis of yst3.
Even though the 2x + 1 portion of Triplo 4 and Triplo 7 did not segregate recessive homozygotes, the segregation ratios in 2x portion and/or total population fit well to 3:1 as shown above. Only the F2 population from Triplo 2 x yst3 showed trisomic ratios in all portions, 2x, 2x + 1 and total.
Telotrisomic analysis was conducted to associate yst3 with the specific arm, 2L or 2S. The results are shown in Table 2.
Table 2. F2 data for telotrisomic analysis of yst and v.
From the data shown in Table 2 it is obvious that the gene yst3 is not associated with the long arm (2L). In the F2 population from Triplo 2S x yst3, the segregation ratio for + : yst3 a 3:1 ratio in the disomic portion and in the total F2 population. Even though the segregation ratio for + : yst3 in the trisomic portion does not appear to fit a 3:1 ratio, the X2 (3:1) value was 3.08 which is a good fit to the disomic ratio. These data suggest that the gene yst3 is not associated with the short arm of chromosome 2 (2S) either.
To test the validity of this experiment, the segregation ratios for Vv for two vs. six-rowed trait were studied. The segregations for V vs. v in Triplo 2L were typical trisomic ratios with no recessive homozygotes in the trisomic portion. The segregation ratio in the total F2 population did not fit a 3:1 ratio (X2 = 10.076). These results confirm that the Vv alleles are located in the long arm and the experiment was carried out correctly. The Vv segregation in the F2 population from Triplo 2S x yst3 v was a typical Mendelian ratio of 3:1 in all 3 portions, 2x, 2x + 1 and total F2 population. The pattern of F2 segregation for + : yst3 is very similar to V : v indicating yst3 and v are not in this arm (2S).
New sets of experiments have been initiated to determine the association of yst3 with specific chromosome and chromosome arm.
2. The gene i for deficiens
The genetic nature of the i gene in relation to the V allele complex has not been completely understood, even though the i gene has been located in the short arm of chromosome 4 (Robertson et al., 1947; Tsuchiya, 1978). Telotrisomic analysis was conducted to associate the i gene definitely with a specific arm of chromosome 4. The genetic stock for the i gene used in this experiment was the most commonly used stock, CSU B4-2, Nudideficiens. Table 3 shows the segregation ratios in F2.
Table 3. F2 segregation ratios from cross between Triplo 4S x CSU B4-2 (i).
The segregation of + : i fits a trisomic ratio of 8 + : 1i (X2 = 0.004) in the disomic portion. The F2 ratios in the 2x portion and total F2 population did not fit a 3+ : 1i ratio with fewer recessive homozygotes than expected. These data suggest a trisomic ratio of segregation for i gene. However, an appreciable number of recessive homozygotes was found in the 2x + 1 portion which showed good fit to a 3+ : 1i disomic ratio. It is extremely difficult to explain these data. More detailed analysis is now underway to determine the association of the i gene with a specific arm.
The data presented in this report showed problems in telotrisomic and/or primary trisomic analysis. New experimental design and new materials are necessary to solve these problems.
References:
Robertson, D.W., G.A. Wiebe and R. Shands. 1946. A summary of linkage studies in barley; Supplement I, 1949-1946. J. Am. Soc. Agron. 39:464-473.
Singh, R.J. and T. Tsuchiya. 1973. Allelison testing among three yellow streak mutants. BGN 3:54-55.
Tsuchiya, T. and J.V. Alanko. 1976. Genetic studies of two mutations by means of primary trisomic analysis. BGN 6:84-85.
Tsuchiya, T. 1978. Linkage maps of barley. 1978. BGN 8:146-150.
