The salivary gland cells in the larval stages of Drosophila contain large, multistranded polytene chromosomes. Polytene chromosomes are produced by repeated replication during synapsis without separation into daughter nuclei. This laboratory procedure outlines the mechanism by which salivary glands are removed and prepared so that the polytene chromosomes may be observed. Drosophila virilis is used instead of Drosophila melanogaster because D. virilis is much larger and it is easier to dissect and remove the salivary glands from the larvae of this species.
Larger larvae are easier to dissect.
However, select an active larva and one that has not started to pupate. Using the stereomicroscope, dissect the larva by placing one teasing needle on the posterior aspect of the larva and the other needle at the anterior end, near the black mouth parts. There are two transparent salivary glands located anteriorly in the larva. The glands are characterized by a granular, bead-like appearance. A narrow, white ribbon of fat surrounds the glands and should be torn away.