title: Differences in the number of nucleolus organizers in Chironomus tepperi shown by in situ hybridization.
abstract: Two stocks of Chironomus tepperi could be isolated. One stock, N(IV)+, contains nucleolus organizers in chromosome I and IV, whereas the other one, N(IV)-, shows only one nucleolus in chromosome I. It is demonstrated by in situ hybridization with radioactive rRNA that the absence of the nucleolus in chromosome IV of stock N(IV)- is not related to an inactivation of the nucleolar DNA, as might have been suggested, but is due to the lack of ribosomal cistrons.
mesh_terms: D000818:Animals; D002466:Cell Nucleolus; D002875:Chromosomes / Q000648:ultrastructure*; D004247:DNA / Q000235:genetics*; D004175:Diptera / Q000235:genetics*; D005796:Genes; D009693:Nucleic Acid Hybridization; D012335:RNA, Ribosomal / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D012335:RNA, Ribosomal; D004247:DNA