BGN 10: Acrocentric chromosome 4S-4L in barley BARLEY GENETICS NEWSLETTER, VOL. 10, II. RESEARCH NOTES
Tsuchiya and Hang, pp. 72-73

II. 32. Acrocentric chromosome 4S4L in barley.

T. Tsuchiya and A. Hang. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.

This work has been supported partly by USDA/SEA Research Grants 12-14-5001265 and 5901-0410-9-0334-0 to the senior author.

In the progeny of a Triplo 4 plant (Robust 2, T1103-4) of Shin Ebisu 16 (S.E. 16), a plant (SE 67-19-19) with 2n = 14 + 1 acrocentric chromosome was found (Tsuchiya, 1971) and called acrocentric trisomic 4A (Tsuchiya, unpublished). The morphology of this acrocentric trisomic 4A was similar to the primary trisomic for chromosome 4 (Triplo 4). The extra chromosome seemed to have one complete arm and proximal part of the other arm with the distal portion missing to make it acrocentric.

In the progeny of the acrocentric trisomic 4A, a telocentric chromosome was found in a telotrisomic condition and called telotrisomic 4A (Tsuchiya, 1971). This telotrisomic was later called Triplo 4S based on the results from telotrisomic analysis of several genes in chromosome 4 (Tsuchiya and Singh, 1973; Singh and Tsuchiya, 1974).

Also, one plant with 2n = 15 + 1 acrocentric 4A chromosome was found in the progeny of the acrocentric trisomic 4A. In the progeny of the plant with 15 + 1 acro 4A chromosome, several plants with 2n = 14 + 1 small telocentric fragment were obtained (Singh and Tsuchiya, 1973). The size and shape of this small extra telocentric fragment was similar to the broken long arm of the acrocentric chromosome 4S4L. At meiotic diakinesis, the extra small telocentric fragment associated with two normal chromosomes to form a hetromorphic trivalent in approximately 80% of sporocytes (Singh and Tsuchiya, 1973).

Based on these results, it was assumed that a fragmentation occurred in the long arm of chromosome 4 (4L) at meiosis in the original primary trisomic (Triplo 4, R2) to produce acrocentric chromosome 4S4L. The acrocentric trisomic condition stimulated further chromosome breakages - misdivision this time - to produce a telocentric chromosome for the short arm of chromosome 4 (Triplo 4S) (Tsuchiya, 1971) and a small telocentric fragment chromosome (Telo 4Lf or telocentric fragment of the long arm of chromosome 4) (Singh and Tsuchiya, 1973). Since these two telocentric chromosomes are produced in two independent incidents, the misdivision may have occurred more than once at the centromere of the acrocentric chromosome.

The present author has suggested a possible radiomimetic effect of Triplo 1S to produce misdivision and other breakages in normal chromosome 1 (Tsuchiya, 1979). Acrocentric trisomic 4S4L condition may also have a radiomimetic effect on the acrocentric chromosome.

The possible radiomimetic effect of the extra acrocentric chromosome may also extend to the other segment of the acrocentric chromosome 4S4L. Hang and Tsuchiya (1980) have found a plant with 2n = 14 + 1 small metacentric chromosome in the F2 population of crosses Acrocentric 4S4L x lg 3 mutant. The size and shape of the extra small metacentric chromosome suggest that breakage might have occurred at the proximal portion of the short arm of the acrocentric chromosome 4S4L, possibly at one of the two proximal heterochromatic bands shown by Giemsa banding technique (Linde-Laursen, 1978a,b).

References:

Hang, A. and T. Tsuchiya. 1980. Linkage mapping of several genes in the long arm of chromosome 4. BGN 10:25.

Linde-Laursen, I. 1978a. Giemsa C-banding of barley chromosomes. I. Banding pattern polomorphism. Hereditas 88:55-64.

Linde-Laursen, I. 1978b. Giemsa C-banding of barley chromosomes. II. Banding patterns of trisomics and telotrisomics. Heredita 89:37-41.

Singh, R.J. and T. Tsuchiya. 1973. Occurrence of small telocentric fragment chromosome in the progenies of a plant with 15+1 Acro 4A chromosome. BGN 3:55-56.

Singh, R.J. and T. Tsuchiya. 1974. Further information on telotrisomic analysis in barley. BGN 4:66-69.

Tsuchiya, T. 1971. Telocentric chromosomes in barley. Barley Genetics II (Proc. 2nd Intern. Barley Genet. Symp.):72-81.

Tsuchiya, T. 1979. Radiomimetic effect of the short arm of chromosome 1 (Telo 1S) in barley? BGN 9:103-105.

Tsuchiya, T. and R.J. Singh. 1973. Further information on telotrisomic analysis in barley. BGN 3:75-78.

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