Abstract
In the present study some observations were made on X-ray induced alterations in the nucleolus-chromosome relationship. The material employed was pollen grains which were derived from X-rayed PMCs. It was shown that (i) alterations in the cellular condition due to irradiation disturb the usual relationship between chromosomes and nucleoli, often so profoundly that every chromosome end may become functional as to the nucleolar organisation, and (ii) by translocations and inversions involving terminal segments, nucleolus-organizing regions come to take intercalary positions, thus giving rise to sat-constrictions in subsequent mitosis.The whole of the present study accordingly furnishes evidence for the assumptions previously made by the writer (No. 6 of this series) on various problems concerning this relationship, viz., the concept of “nucleolar chromosomes”, the competition hypothesis of the nucleolar organisation and the origin of sat-chromosomes.
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