Polytene chromosome preparation

Protocol 6.1 Dissection of Larval Salivary Glands and Polytene Chromosome Preparation, 111... 

A large number of different food media have been used for the culture of D. melanogaster. Several are described by Ashburner and Thompson (1978), Ashburner (1989b), Roberts and Standen (1998), and on the Bloomington Stock Center Web Site http //fly.bio.indi-ana.edu/media.recipes.htm. Only two are described below a general-purpose medium, and one suitable for growing larvae for polytene chromosome preparations. Table 35.2 lists the sources of ingredients used in the preparation of these media. In addition, instant media are available commercially (see Table 35.2). 

Single-copy probes can also be tested on squash preparations of polytene chromosomes (see Pardue, this volume). 

Polytene chromosomes are found in several larval and adult tissues, but preparations are usually made of the chromosomes in the larval salivary glands, because the glands are easily dissected and the polytene chromosomes are large. 

Heat the staining solution (but do not boil) and filter. If stored tightly capped, it will last for many years. The same solution, but without the orcein stain, can be used to prepare polytene chromosomes for in situ hybridization. 

Note Time of exposure depends on the probe and the target. For single-copy X clones on polytene chromosomes, a 24-hour exposure is usually enough. Prepare several slides so that different exposures can be checked. 

Preparation of polytene chromosomes for in situ hybridization Protocol 25... 

Preparation of spread polytene chromosomes for electron microscopy Protocol 37... 

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