II.14. Telotrisomic studies for locating genetic control of chromosome elimination.
K. M. Ho and K. J. Kasha, Crop Science Department, University of Guelph, Guelph, Ontario, N1G 2W1 Canada.
Footnote: Based on the existing linkage map and the telotrisomic analysis of marker stocks, it was concluded that the telo 3 is telo 3S. (cf. BGN 4:68 ). Editors.
Earlier studies have led to the conclusion that chromosomes 2 and 3 of H. vulgare control chromosome elimination in interspecific hybrids of H. vulgare and H. bulbosum (Kasha et al., 1972; Barclay et al., 1972). For locating more precisely the arms of these chromosomes exhibiting control over chromosome elimination, the crosses between monotelotrisomic of these chromosomes and tetraploid H. bulbosum were carried out.
Since monotelotrisomic plants produced two kinds of gametes, one with 7 and the other with 7 plus telo, two types of hybrid progeny are expected from such crosses: (1) 21 chromosome triploid hybrids produced when the 7 chromosome gamete is transmitted; and (2) 21 plus telosome hybrids produced when the 7 plus 1 telo gametes are transmitted. If the specific telosome carries a factor controlling chromosome stability, the 21 plus telosome hybrids will not survive or will be rare in such crosses. In such instances, one might expect to find a plant with 7 chromosomes plus a telosome if it is viable.
Four monotelotrisomic lines in diploid H. vulgare were used in this study (Table 1). One had been identified as being the long arm of chromosome 2 (Telo 2L) and a second as the long arm of chromosome 3 (Telo 3L), although the latter identification may not be as certain (Tsuchiya and Singh, 1973).
Table 1. The designation and source of monotelotrisomic lines in diploid H. vulgare.
Telo 2C and Telo 2D were found at Guelph in the progeny of primary Trisomic 2 and are thus most likely monotelotrisomic for one of the arms of chromosome 2. Neither has yet been identified with marker genes.
The results of crosses between four monotelotrisomic lines of H. vulgare and tetraploid H. bulbosum are given in Table 2. The frequency of 21 plus telosome hybrid progeny was similar to the expected frequency of telosomic transmission for Telo-3L, indicating that there is no major factor in the long arm of chromosome 3 controlling chromosome elimination.
The frequency of hybrid progeny with 21 plus a telosome from Telo-2L was quite high (11%) but still much lower than the expected frequency (32%, X2 = 14.76 with 1 df). It would appear that the long arm of chromosome 2 has a significant effect on chromosome elimination. Both Telo 2C and Telo 2D definitely influenced the level of chromosome elimination as did the parent from which they originated, a primary trisomic for chromosome 2. Telo 2D is most likely telosomic for 2L since it was similar to Telo-2L in plant morphology and the level of chromosome elimination expressed. Telo 2C is probably trisomic for the short arm of chromosome 2 and although the number of progeny obtained is small, one plant with 7 chromosomes plus a telosome was found.
In conclusion, there may be at least 3 factors influencing chromosome elimination since it is most likely that the short arm of chromosome 3 and both the long and short arms of chromosome 2 carry genetic factors.
References:
Barclay, I. R., K. W. Shepherd, and D. B. H. Sparrow. 1972. Control of chromosome elimination in Hordeum vulgare - H. bulbosum hybrids. BGN 2:22-24.
Kasha, K. S., E. Reinbergs, W. A. Johns, N. C. Subrahmanyam and K. M. Ho. 1972. Barley haploid studies. BGN 2:36-41.
Tsuchiya, T. and R. S. Singh. 1973. Further information on telotrisomic analysis in barley. BGN 3:75-78.
