Whole mount squash of polytene chromosomes from Drosophila salivary gland. Low magnification survey image of a cluster of chromosomes showing a series of bands and interbands was taken with a High Voltage EM.
Salivary glands from 3rd instar larvae of Drosophila melanogaster were dissected, fixed with formalin-acetic acid containing 0.1% Triton-X 100, and squashed on a glass slide. After freezing in liquid nitrogen, the cover slips removed, and the slide thawed and stained with 1% uranyl acetate, rinsed in 50% ethanol, dehydrated and transferred to amyl acetate, and covered with 2% parlodion in amyl acetate. Selected areas of the parlodion film, are transferred to formvar coated EM grids, and the parlodion removed by immersion in amyl acetate (see Ris H, 1981 Stereoscopic Electron Microscopy of Chromosomes, Meth Cell Biol 22:77-96). Grids were observed using the Madison High Voltage Electron Microscope at 1 MeV.
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