Chromosome Fine Structure: Electron Microscopy of Unfixed, Negatively Stained Human Chromosomes

Abstract

Human chromosomes were obtained from lymphocyte cultures, some of which were incubated with colchicine to provide metaphase chromosomes. After treatment with hypotonic sodium citrate solution, the cells were spread on an air-water interface. Chromosomes were picked up on carbon coated electron-microscope grids and negatively-stained with 2% phosphotungstic acid.
Chromosomes treated in this way tend to distort or fragment, but some are sufficiently well preserved to be identified with their light microscope equivalents. The negative stain enables good resolution of fine structure. The basic structural unit appears to consist of two closely coiled microfibrils some 45-60Å diameter. These appear to be irregularly wound into quaternary coils in the condensing chromosomes.