Electron microscopic band-interband pattern of polytene chromosomes in Drosophila nasuta albomicans. 1. Salivary gland chromosome 2R

The band-interband pattern of salivary gland chromosome 2R in Drosophila nasuta albomicans (division 53-83) was studied by light (LM) and electron microscopy (EM) using squash preparations and surface-spread polytene (SSP) chromosome preparations, respectively. LM and EM maps were compiled. Based on the digitized EM patterns of five homologous SSP chromosomes a computerized chromosome map was plotted. The EM pattern analysis showed a total number of 662 chromosome bands with an almost 98% increase compared with the LM analysis of squash preparations. The majority (about 92%) of interband lengths in SSP chromosome 2R ranged between 0.25 and 0.64 microns, which equal about 0.8-2.1 kb of totally extended DNA or 2.5-6.4 kb of DNA, if a DNA packing ratio of 0.1 microns/kb is assumed for the interbands of SSP chromosomes.