Polytene Maps

The assignment of alpha-numeric to salivary-chromosome band in universal use in the Drosophila community is that of C. B. Bridges, and the maps to use for final assignments of breakpoints are the high-resolution drawings originally published in refs. 2-6 and reprinted in both ref. 7 and ref. 8 (Academic Press also sells a booklet of just the maps separately). Some form of these maps should be available at the microscope for direct comparison with the actual preparation. However, these high-resolution maps are only useful once you know where in the genome you are—they are of too high magnification for scanning work. A low-resolution map of all five arms is also vital to have with you at the microscope; in my experience, both in my own work and in teaching salivary analysis to others, the very best map to use to find your way between and along the arms is the low-magnification drawing of Bridges (9) (reproduced as Fig. 1). Although they are occasionally useful, I do NOT recommend using Lefevre's photographs (1) for routine work. Bridges's drawings are averages of what the banding patterns look like; Lefevre's photographs are of only one cell (for each section) and are badly overstained anyway—they had to be, for the photography, but you do not want to be emulating that! Rather, you should aim at just enough staining to be able to see the bands. How long to stain has to be determined empirically (different batches of stain vary substantially) and also depends on the ambient temperature but is normally between 5 and 10 min. Moreover, many regions were revised between the low- and the

Drosophila Melanogaster Chromosome Map
Fig. 1. (A-F) The 1935 low-magnification map of Drosophila melanogaster salivary chromosome bands originally published by Bridges (2); for use, photocopy each
Fig. 1. (continued) of the segments and assemble them into one long map. (Reprinted with the permission of Oxford University Press from ref. 9.)
Chinese lanterns

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