DNA REPRESENTATION OF VARIEGATING HETEROCHROMATIC P-ELEMENT INSERTS IN DIPLOID AND POLYTENE TISSUES OF DROSOPHILA-MELANOGASTER

Position-effect variegation (PEV) is the mosaic expression of a euchro matic gene brought into juxtaposition with heterochromatin. Fourteen d ifferent transformed Drosophila melanogaster lines with variegating P- element inserts were used to examine the DNA levels of these transgene s. Insert sites include pericentric, telomeric and foul th chromosome regions. Southern blot analyses showed that the heterochromatic hsp26 transgenes are underrepresented 1.3- to 33-fold in polytene tissue rel ative to the endogenous euchromatic hsp26 gene. In contrast, the heter ochromatic hsp26 transgenes are present in approximately the same copy number as the endogenous euchromatic hsp26 gene in diploid tissue. It appears unlikely that DNA loss could account for the lack of gene exp ression in diploid tissues seen with there examples of PEV.