ELECTRON-MICROSCOPIC ANALYSIS OF THE BANDING-PATTERN IN THE SALIVARY-GLAND CHROMOSOMES OF DROSOPHILA-MELANOGASTER - DIVISIONS 11 THROUGH 20OF X

The banding pattern of the proximal half of the polytene salivary glan d X chromosome of Drosophila melanogaster was studied using thin secti on electron microscopy. The bands were identified according to Bridges ' revised light microscopic map. On Bridges' map, the divisions 11 to 20 contain 112 single bands and as many as 181 double bands. A majorit y of Bridges' single bands were identified in the thin sections. A tot al of 23 Bridges' single bands (and 4 bands of division 20) could not be found; in particular, bands were missing from the difficult regions 11DE, 15A, 15C and 16A. Electron microscopy showed the existence of 1 8 additional faint bands, 4 at the region 18D and 7 at 19EF. Bridges' faintest single bands and the new bands were best seen in formaldehyde fixed material. About 1/4 of Bridges' double bands were found to be m ade up of two separate bands each. The remaining Bridges' doublets inc lude all kinds of bands: broad, narrow, dark, faint, puffed. Many of t hem look single in thin sections.