Polytene chromosomes from Drosophila melanogaster, observed from squash preparations, and chromosomes from Chironomus thummi thummi, investigated under physiological conditions, are imaged using an Atomic Force Microscope. Various chromatin fiber structures can be observed with high detail in fixed chromosomes and correspond to structures which are also observed in chromosomes of diploid cells. Unfixed chromosomes can be imaged in buffer and show less fiber-like details because of the inherent soft nature of the chromatin material.
de Grauw, C. J., Avogadro, A., van den Heuvel, D. J., van der Werf, K. O., Otto, C., Kraan, Y., ... Greve, J. (1998). Chromatin Structure in Bands and Interbands of Polytene Chromosomes Imaged by Atomic Force Microscopy. Journal of structural biology, 121(1), 2-8. https://doi.org/10.1006/jsbi.1997.3929