By using a fluorescence in situ hybridization technique we revealed that for nine different q-arm telornere markers the positioning of chromosomes in human G1 interphase nuclei was chromosome size-dependent. The q-arm telomeres of large chromosomes are more peripherally located than telomeres on small chromosomes. This highly organized arrangement of chromatin within the human nucleus was discovered by determining the x and y coordinates of the hybridization sites and calculating the root-mean-square radial distance to the nuclear centers in human fibroblasts. We demonstrate here that global organization within the G1 interphase nucleus is affected by one of the most fundamental physical quantities-chromosome size or mass-and propose two biophysical models, a volume exclusion model and a mitotic preset model, to explain our finding.
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