Chromosomal distribution of the major insert inDrosophila melanogaster28S rRNA genes

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Abstract
SUMMARY: The major type I insert sequence for the 28S rRNA genes ofDrosophila melanogasterhas been mapped within the chromosomes using a probe synthesized from a cloned sequence containing the entire 5·4 kb segment. The genomic distribution was shown to be complex in that the insert sequence occurred next to many different types of sequences, in addition to occurring as an insert in the 28S rRNA genes of theXchromosome.In situhybridization of mitotic chromosomes showed most of the insert units not contained in the ribosomal genes to be located near the ribosomal gene cluster on theXchromosome. Additional sites were detected in polytene chromosomes in region 102C, 8–12 and in the hetero-chromatin of the autosomes.