A Database for Triticeae and Avena
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unpublished).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).
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
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.
BGN 10 toc
BGN Main Index