ELECTRON-MICROSCOPIC STUDIES ON POLYTENE CHROMOSOMES OF CHIRONOMUS-THUMMI SALIVARY-GLANDS .1. ULTRASTRUCTURAL MAPPING

The method of ultrathin sections of unsquashed salivary gland polytene chromosomes of Ch. thummi was applied to their ultrastructural mapping. There was a good agreement between electron micrographs and Hagele''s light microscopic map (1970) with respect to the pattern and number of bands. Bands (94%) were identified in larval and prepupal chromosomes. In Ch. thummi, band thickness varied from 0.05-0.5 .mu.m. Most characteristic were 0.2-0.3 .mu.m bands. Morphologically, bands were classified as: continuous (frequently with holes and gaps), discrete, dotted and continuous-discrete and discrete-dotted. Band morphology is related to band size, such that smaller bands were also dotted. Bands beginning to puff likewise became dotted. Interbands in unsquashed chromosome sections were from 0.05-0.15 .mu.m. The smallest interbands contained only fibrils, in the larger interbands few granules could be observed. This makes interbands distinguishable from a typical puff with many such granules.