Scanning Microscopy


Chromosomes and chromosome fragments from embryonic offspring of a transgenic rainbow trout were examined using scanning electron microscopy (SEM). SEM is an extremely useful technique for studying the structure of chromosome fragments since little morphological detail is revealed by conventional staining methodologies and light microscopy. The chromosome preparations were processed for SEM by combining an osmium-thiocarbohydrazide-osmium (OTO) technique with 2-4 nm of gold deposition. This technique revealed the organization of individual chromatin fibers in chromosome fragments and intact chromosomes. Both a linear chromosome fragment with a width similar to that of an intact chromatid (approximately 0.60 micrometers) and a spherical chromosome fragment with a diameter slightly greater than the width of an intact chromatid (0.66 micrometers) were observed in metaphase chromosome preparations. A connective fiber (200-300 nm in diameter) between a chromosome fragment and a host chromosome was observed. Interconnecting fibers (approximately 30 nm in diameter) between chromosomes, between chromosomes and fragments, and between sister chromatids were observed in every cell examined. We conclude that SEM permits a detailed analysis of chromosome fragment structure and the nature of chromosome-fragment associations that cannot be obtained using conventional light microscopy techniques.

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