Electron microscopic analysis of the banding pattern in the salivary gland chromosomes of Drosophila melanogaster. Division 1 and 2 of X

Abstract

Electron microscopic analysis of the divisions 1 and 2 in the salivary gland chromosome X of Drosophila melanogaster reveals at least 100 recognizable bands. This number is ca. 75 % higher than the respective number of those bands drawn by Bridges (1935) in his original light microscopic reference map, ca. 15 % higher than given by Bridges (1938) in his revised map of the X chromosome, and ca. 78 % higher than revealed by earlier electron microscopic analyses of the same divisions. The main difficulty in comparison of results with Bridges' maps has been the definition of real structural double bands. According to our interpretation only about 80 % of Bridges' doublets in division 1 and 2 are double structures also in the electron micrographs. Possible reasons for the high number of double bands in Bridges' maps and, on the contrary, for too low number of bands revealed by some earlier EM studies are discussed.