Mechanisms of chromosome banding : VI. Whole mount electron microscopy of banded metaphase chromosomes and a comparison with pachytene chromosomes

Chinese hamster chromosomes, banded by exposure to actinomycin D during the G 2 period, were examined by whole mount electron microscopy. Bands of condensed chromatin were present in unstained preparations that were not fixed with methanol-acetic acid indicating that the differential condensation of chromatin plays a role in banding by this technique. There was a tendency for interdigitation of the chromatin of the homologous bands on sister chromatids. Since previous studies had shown that the bands of mitotic chromosomes matched the chromomeres of meiotic chromosomes, whole mount electron microscope preparations of pachytene chromosomes were also examined. These suggest that in addition to condensation the chromatin of the chromomeres may also have a higher density of attachment sites to the lateral element of the synaptonemal complex, and probably to the nuclear membrane in interphase cells.