title: Insights on plant chromosome structure provided by the FPG technique.
abstract: The high resolution afforded by the fluorescence plus Giemsa (FPG) labelling method has allowed us to visualize three main features in BrdU-substituted A. cepa chromosomes. These are (1) exchanged segments smaller than the width of the chromatid detected after BrdU substitution for two S periods; (2) late-replicated chromosome segments (LRS) of similar characteristics; (3) discontinuous or 'step-wise' exchanges (SWE). A variation in longitudinal dimension has not been observed in any case; all these features have a roughly constant longitudinal dimension of about 0.5 microns. These results suggest that arrangements of the chromatin fibres having a diameter detectable under the light microscope following a longitudinal pattern can be ignored. In addition, our observations seem to support the model of a coiled structure of metaphase chromosomes. On the other hand, the analysis of the morphological pattern shown by the SWE along a chromatid and in sister chromatids has provided us with what could be evidence of a direction of the hypothetical gyres.
mesh_terms: D001399:Azure Stains; D002875:Chromosomes / Q000648:ultrastructure*; D005453:Fluorescence; D008722:Methods; D010944:Plants / Q000235:genetics*
chemical_list: D001399:Azure Stains