In situhybridization of nucleotide sequence toDrosophila melanogasterinterphase polytene chromosomes was initially developed by Pardue, who has published an extensive account ofDrosophilapolytene chromosomes and hybridization to these chromosomes (1 ). The procedure, which used radioactively labeled probes, was later adapted to allow the use of more sensitive and safer nonradioactive labeling methods (2 ). The method has been used extensively for gene mapping and identification of transposable element insertion sites.In situhybridization to chromosomes has also been performed in cross-species studies within Diptera to give valuable evolutionary information, including conservation of linkage groups, and to identify homologous genes in related species (3 -5 ). In addition, there have been recent advances that extend this technique to salivary gland preparations from stored fixed specimens (6 ).
