Computerized EM maps of surface spread polytene chromosomes 1 digitizing and plotting of banding patterns

A standard plotting program for the band-interband pattern of polytene chromosome maps was written in EXTENDED BASIC for a pocket computer coupled to a plotter (Sharp PC-1500 + CE-150). In this program, the individual polytene structure (i.e. one chromosome band and its right-handed interband) was digitized using a set of variables: [A] band diameter, [B] band type (solid, dotted, straight or curved bands), [C] band thickness, [D] interband length, [E] interband as well as puff and Balbiani ring outlines, [R] radius (for curved bands), [W] sectioning (of the pattern in chromosome maps) and [V$] reference numbers. The general use of this technique was tested by digitizing and computerized plotting of data from hand-drawn chromosome maps in Chironomus and Drosophila. Electron micrographs of surface spread polytene (SSP) chromosomes from the salivary glands of Chironomus thummi larvae were used to digitize the pattern of region F1-4 in chromosome I. The computerized EM map of this region was compared with the LM map from chromosome squash preparations.