localisation of non-replicating heterochromatin in polytene cells of Drosophila nasuta by fluorescence microscopy

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Abstract
A simple fluorescence technique is decribed to localise in situ the non-replicating alpha heterochromatin in the chromocentre region of Drosophila nasuta polytene nuclei. After incorporating 5-bromodeoxyuridine in larval salivary gland cells for one or two cycles of replication, the polytene nuclei are examined for Hoechst 33258 flourescence at pH 7.O. The nonreplicating alpha heterochromatin remains brightly fluorescing as it does not incorporate any 5-bromodeoxyuridine while the rest of the replicating chromatin shows dull fluorescence due to the quenching of Hoechst 33258 fluorescence by the bromodeoxyuridine substituted DNA.