Mechanism of Chromosome Elimination,Hordeum Hybrids,N.C. Subrahmanyam,K.J. Kasha,Cytological Study,Hybridization Programmes,Mitotic Cycle,Chromosomes,M.D. Bennett

	Mechanism of Chromosome Elimination - The Mechanism of chromosome elimination in Hordeum hybrids was studied by N.C. Subrahmanyam and K.J. Kasha (1973) and by M.D. Bennett and his associates (1976). The following conclusions were made: (i) normal double fertilization occurs in interspecific crosses as confirmed through cytological study; (ii) after fertilization, there is a gradual and selective elimination of H. bulbosum chromosomes from nuclei of endosperm as well as embryo cells, so that eventually haploid embryos are produced. No evidence of the elimination of H. vulgare chromosomes was available.
Differences were, however, observed in the rates of chromosome elimination and these were attributed to genotypic differences in the stocks used in hybridization programmes. In 1970's, M.D Bennett and his coworkers, then at Combridge (U .K), had examined the possible causes of chromosome elimination and concluded that sudden shortage of proteins in the developing embryo and endosperm, and the better ability of vulgare chromosomes to form spindle attachments relative to bulbosum chromosomes may be responsible for elimination of the bulbosum chromosomes. Other possible causes like differences in mitotic cycle, congression during mitosis, etc. were ruled out by them.
It has also been demonstrated that the elimination of bulbosum chromosomes is under genetic control. 80 and Kasha (1975) used primary trisomics and monotelotirsomics in crosses with tetraploid H. bulbosum and concluded that both arms of chromosome 2 and the short arm of chromosome 3 of H. vulgare are responsible for chromosome elimination although their effect may be neutralized or offset if sufficient dose of bulbosum chromosomes is available. The effect of these vulgare chromosomes, however, will be indirect.