Transversal banding pattern
A Transversal banding pattern of the polytene chromosomes could not be observed regularly but only rarely in about one to two chromosomes per nucleus. The pattern usually does not expand the entire length, but was restricted only to part of the chromosome (figure a) and variable size.
The typical composition of polytene chromosomes consisting of numerous chromatids laying densely and more or less parallel side by side is in general not visible in the light microscope due to it's low resolution. Sometimes, however, when the euchromatin in very decondensed, and especially the one of chromosome A, it can let imagine the bundling of many chromatids (figure b).
Scale bar represents 10 µm.