title: Cytogenetic and molecular aspects of position effect variegation in Drosophila melanogaster. II. Peculiarities of morphology and genetic activity of the 2B region in the T(1;2)dorvar7 chromosome in males.
abstract: The peculiarities of compact blocks appearing as a consequence of position effect variegation were studied in male polytene chromosomes. In T(1;2)dorvar7/Y males the frequency of nuclei with a block in the 2B region was lower at all temperature and the chromosome region involved in compaction was shorter than in T(1;2)dorvar7/FM6 females. The fraction of nuclei with blocks was considerably increased in dorvar7/0 males, especially at 18 degrees C when the viability of these males is sharply reduced. The following features distinguish the blocks in males from those in females: (i) compaction of the 2B region in the males results in genetic inactivation only to a very small extent; (ii) the structure of the blocks in males is diffuse; and (iii) the male blocks still maintain some transcriptional activity as indicated by 3H-uridine incorporation. The temperature-sensitive period of both block formation and genetic inactivation was found to be during the first 3 h of embryonic development.
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000378:metabolism / Q000648:ultrastructure; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D008297:Male; D008854:Microscopy, Electron; D010641:Phenotype; D013696:Temperature; D014178:Translocation, Genetic; D014529:Uridine / Q000378:metabolism; D014998:Y Chromosome
chemical_list: D014529:Uridine