II. 29. Preliminary studies on identification of telocentric chromosomes in telotrisomic barleys by Giemsa N-banding technique. (1)
R. J. Singh and T. Tsuchiya, Department Agronomy, Colorado State University, Fort Collins, Colorado 80523 U.S.A.
(1) Supported in part by US3A/SEA Competitivc Rescarch Grant 5901-0410-90334-0 to T. Tsuchiya.
An improved Giemsa N-banding technique (Singh and Tsuchiya, 1981a) was used to identify nine telotrisomics (Triplo 1L, 1S, 2L, 2S, 3L, 3S, 4L, 5L and 6S) of barley. The Giemsa N-banding technique revealed that the telocentric chromosome in Triplo 1L carried only a centromeric band, while telo 1S had centromeric and two intercalary bands, the band proximal to the centromere was darker than the one towards telomere. In earlier publications the long arm was considered to have centromeric and two intercalary bands and the short arm with a centromeric band only (Islam 1980, Linde-Laursen 1978, Noda and Kasha, 1978).
The Giemsa N-banding pattern of telo 2L indicated that this telocentric chromosome carried a centromeric and an intercalary band that is similar to the banding pattern of the long arm of chromosome 2. Telo 2S carried a centromeric band, two intercalary bands and a terminal band. These bands were observed on the short arm of chromosome 2. While working with the Giemsa N-banding pattern of Triplo 2S, it was found that in one plant (Telo 80-32-7), the telocentric chromosome was smaller than the normal short arm of chromosome 2. The banding pattern and karyotype analysis revealed that about 30% of the short arm has been deleted. If such type of telotrisomic plants were used in genetic/linkage analysis, a wrong conclusion will be drawn because the genes located on the deficient segment will show a disomic ratio.
The morphological appearance and banding pattern of the telocentric chromosome for chromosome 3 indicated that it is similar to the long arm. However, this particular telocentric chromosome was designated as telo 3S because it showed association with the genes located on the short arm of the linkage map (Robertson 1971) of chromosome 3 (Singh 1974, Tsuchiya and Singh 1981). Recently the isolation of telo 3S from the selfed progenies of a plant with the chromosome number 13 + 1 acro 3L3 - 1 telo 3S (Singh and Tsuchiya 1981b) confirmed that the earlier identified telo 3S is telo 3L which carried a centromeric band and also an intercalary band. However, telo 3S carried only a dark centromeric band. The present study thus demonstrates that the linkage map prepared by Tsuchiya (1980) should be reversed, long arm to short arm and vice versa.
The banding pattern of telocentric chromosome 4S at first revealed that it does not belong to the long or short arm. Critical observations on karyotype and banding pattern suggested that the telocentric chromosome is the long arm and it possesses a deficiency for a distal euchromatic segment. Genetically, this telocentric chromosome was previously identified as a short arm (telo 4S) because two genes in the short arm of the linkage map of chromosome 4 (f9 for chlorina seedling 9 and K for Hooded lemma), showed a trisomic ratio (Singh 1974, Tsuchiya and Singh 1981). This suggests that the linkage map of chromosome 4 (Tsuchiya 1980) should also be reversed.
The karyotype analysis and the banding pattern of telo 5L indicated that the telocentric chromosome belongs to the long arm of chromosome 5 which carried a centromeric band and an intercalary band. This confirms the results of Tsuchiya (1972a).
Telo 6S was readily identified and carried only a centromeric band. This confirms the previous report of Seip (1980).
The telocentric chromosomes of barley were designated on several occasions (Table 1). The original arm designation was mainly based upon the morphological characteristics of telotrisomic plants and genetic/linkage analysis. The application of the improved Giemsa N-banding technique provided the precise identification of telocentric chromosomes of barley. The proposed designation and previous designations were shown in Table 1.
Table 1. Proposed and previous designation of telotrisomic types in barley.
References:
Fedak, G., T. Tsuchiya and S. B. Helgason. 1971. Cytogenetics of some monotelotrisomics in barley. Can. J. Genet. Cytol. 13:760-770.
Fedak, G., T. Tsuchiya and S. B. Helgason. 1972. Use of monotelotrisomics for linkage mapping in barley. Can. J. Genet. Cytol. 14:949-957.
Islam, A.K.M.R. 1980. Identification of wheat-barley addition lines with N-banding of chromosomes. Chromosoma (Berl.) 76:365-373.
Linde-Laursen, Ib. 1978. Giemsa C-banding of barley chromosomes I. Banding pattern polymorphism, Hereditas 88:55-64.
Noda, K. and K. J. Kasha. 1978. A proposed barley karyotype revision based on C-band chromosome identification. Crop Sci. 18:925-930.
Robertson, D. W. 1971. Recent information of linkage and chromosome mapping. Barley Genetics II. (Proc. IInd Intern. Barley Genetics Symp.) 220-242.
Seip, L. 1980. The telotrisomic for the short arm of chromosome 6 in barley. M.S. Thesis, Colorado State Univ., Fort Collins, C0, USA.
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Singh, R. J. and T. Tsuchiya. 1977. Morphology, fertility, and transmission in seven monotelotrisomics of barley. Z. Pflanzenzuchtg. 78:327-340.
Singh, R. J. and T. Tsuchiya. 1981a. An improved Giemsa N-banding technique for the identification of barley chromosomes. Chromosoma (Berl.).
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Tsuchiya, T. 1971. Telocentric chromosomes in barley. Barley Genetics II. (Proc. IInd Intern. Barley Genetics Symp.) p 72-81.
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Tsuchiya, T. and R. J. Singh. 1981. Chromosome mapping in barley by means of telotrisomic analysis. Theor. Appl. Genet. (In press).
