ABSTRACT
The introduction of electron microscopy in the study of ultrastructure has helped to clarify chromosome structure at the submicroscopic level. For the preparation of materials to be observed under the electron microscope, the following steps should be adopted under strictly controlled conditions: fixation, dehydration, embedding, sectioning and mounting. Several methods have also been developed for fixation and embedding in situ, thus avoiding any distortion or displacement of the structure. The fixation and dehydration of monolayers attached to coverslips are carried out in staining dishes before final embedding in epon or other media using a silicone rubber mould. The procedure involves glutaraldehyde fixation, dehydration in hydroxypropyl methacrylate and in situ embedding in epon. For negative staining and positive contrast of whole mounted chromosomes, place a drop of 2% phosphotungstic acid at pH 7 on the grid with chromosomes after chromosome isolation and centrifugation through isolation buffer.
