Abstract
The human C group chromosomes late to start replication in asynchronous and in FUdR synchronized cell lines are X chromosomes. These same chromosomes are also heterochromatic during interphase. During metaphase these allocyclic Xs cannot be identified simply by metaphase position or morphology and show a wide range of measurements for arm ratio, centromere index and total length. Replication starts in the short arm and extends over the entire chromosome during the 2nd and 3rd hr of S until by the 4th hr distinction from other C group chromosomes cannot be made by means of the labeling pattern. When the allocyclic X chromosomes start replication the pattern of H3TdR label over interphase sex chromatin and non-specific heterochromatin shifts from unlabeled to labeled in FUdR synchronized human cell lines. The overall time required for replication of the allocyclic X is less than that for the other chromosomes in both asynchronous and FUdR treated cells. A hypothesis is presented for a direct relation between the delay of onset of replication in heterochromatin and its degree of interphase condensation.
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The present study was supported by research grants: No. HD-00777 from the National Institutes of Health and No. E-487 from the American Cancer Society, Inc.
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Priest, J.H. The replication of human heterochromatin in serial culture. Chromosoma 24, 438–455 (1968). https://doi.org/10.1007/BF00285018
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DOI: https://doi.org/10.1007/BF00285018