| Pairing between the two arms of the same chromosome
in nulli-5b haploid plants of Chinese Spring Mahesh D. UPADHYA Central Potato Research Institute, Simla-1, India In the earlier report on the meiotic behaviour of nulli-5B haploid plants (UPADHYA and SWAMINATHAN 1967), an interesting observation was left out. It was observed that in 54% of the total 173 miocytes analysed from the two plants, a maximum of three chromosomes showed pairing between their two arms like an isochromosome (Fig. 1). Since these two plants were isolated from the progeny of the cross between a single plant of mono-5B and rye, the meiotic preparations from 27- and 28-chromosome hybrids should have also shown the presence of up to three isochromosomes if the three chromosomes in nulli-5B haploid plants were to be isochromosomes. However, none of the 27- or 28- chromosome hybrids analysed showed the presence of any isochromosome. Hence, it is certain that the two nulli-5B hyploid plants did not have any isochromosome in their constitution. The above observations thus show that in haploid condition, when the critical chromosome 5B is absent, there are at least three chromosomes which show pairing between their two arms. This would indicate a certain degree of homoeology between the two arms of these three chromosomes. However, these three chromosomes do not show similar behaviour in the 5B deficient 27-chromosome wheat-rye hybrids. It is possible that in 5B deficient 27-chromosome plants the presence of rye genome in some way modifies the effect of 5B deficiency realizable in the nulli-5B haploid plants. It is, therefore, indicated that in Chinese Spring there are at least three chromosomes which carry certain degree of genetic duplication in their two arms. If this is true, then in future these observations would be of significance in genetic mapping of chromosomes in Chinese Spring, and in the interpretation of data on chromosome pairing utilizing telocentrics, specially in the absence of chromosome 5B. Literature UPADHYA, M.D. and M.S. SWAMINATHAN 1967. Biol. Zantral. 86 : 239-255. (Received April 1, 1969) |