Polytene chromosomes observed scanning electron microscope.

Polytene chromosomes of the salivary gland cells from Drosophila melanogaster were observed by means of scanning electron microscopy using mainly the cracking method. Band and interband regions were visible as transverse striped patterns consisting of multiple, side-by-side fibres. Band regions seemed much more compact than interband ones. In the cross section of the entire chromosome, about 1,100 chromatid fibres could be counted. Intranuclear fine filaments could be recognized surrounding the polytene chromosomes each of whose diameters were almost the same (160--200 A). Field emission scanning electron micrographs showed the unit chromatid fibres clearly in very high magnification.