Mobile dispersed repeated DNA elements in the Drosophila genome.

The molecular and cytogenetic organizations of 19 nonhomologous dispersed repeated sequence families were studied in 15 different laboratory strains of Drosophila melanogaster. Elements from each of the families appear to undergo transposition within the Drosophila genome, because there were striking differences in both the number and chromosomal locations of these elements between strains. A significant fraction (greater than 1%) of Drosophila DNA therefore has an unstable genomic organization. Each middle repetitive family exhibited similar variations in the chromosomal distribution of elements between the strains. Although the movements of these elements are not limited to a small number of genomic sites, there are chromosomal regions where elements from the different dispersed repeated DNA families appear to be clustered. The locations of such preferred integration sites are different in each of the D. melanogaster strains examined.