Selection and Transposition of Mobile Dispersed Genes in Drosophila melanogaster

Recently, a peculiar class of genes was discovered during the cloning of DNA fragments in the genome of Drosophila melanogaster. These genes include several families and are normally represented by dozens of identical copies scattered over the genome (Georgiev et al. 1977; Finnegan et al. 1978; Ilyin et al. 1978). They may be localized in the polytene chromosomes by means of in situ hybridization. The main distinction of these genes is their highly varying location in different stocks, mainly coinciding with the regions of intercalary heterochromatin in the polytene chromosomes (Georgiev et al. 1977; Ananiev et al. 1978). These genes are intensively transcribed; corresponding poly(A)+ RNA transcripts belonging to the abundant classes of cytoplasmic RNA can be detected in the cytoplasm of cultured Drosophila cells (Finnegan et al. 1978; Ilyin et al. 1978). These genes have been termed mobile dispersed genes (mdg) (Tchurikov et al., this volume).