Electron micrograph map of the Drosophila melanogaster polytene chromosome 3R divisions 91 through 100.

The banding pattern of the distal half of the polytene salivary gland 3R chromosome of Drosophila melanogaster was studied by means of the thin section electron microscopy. Bands were identified according to the revised light microscopic map of Bridges. Bridges' map contains 332 single bands and 137 double bands within the region 91 through 100. This makes a total of 606 bands when the doublets are counted as two bands each, but 469 bands when the doublets are counted as one band. In the electron micrographs we found a total of 443 bands within this region. 109 Bridges' singlets were easily detected in almost all thin sections, while 144 mainly faint bands could be seen only in some micrographs. 79 Bridges' single bands and one doublet (94D7-8) could not be found. 42 Bridges' doublets were made up of two separate bands each, 87 Bridges' doublets looked single, and three pairs of Bridges' doublets formed dark complexes in the thin sections. The telomere region with the most distal band 100F4-5 was gray. A total of 15 new bands, which are not drawn on Bridges' map, were detected. Most of the new bands were in the divisions 96 and 99.