ASYNCHRONOUS DNA SYNTHESIS OF SEX CHROMATIN IN HUMAN INTERPHASE NUCLEI

Abstract

Cultured normal human peritoneal cells were exposed to tritiated thymldine. Radioautographic stripping film was applied to the preparations for three weeks before being developed. Examination of the pattern of labelling showed that in approximately 3% of labeled nuclei there was a localized concentration of grains at the periphery of the nucleus. The findings were consistent with specific labeling of heterochromatin corresponding to at least a portion of a late-replicating X chromosome or possibly an entire X chromosome in some nuclei. In conjunction with evidence shown by other authors the data suggest that the sex chromatin body, which is located at the periphery of the nucleus, is formed by a portion of a late-replicating X chromosome.