Analysis of a dispersed repetitive DNA sequence in isogenic lines of Drosophila.

The location of sequences homologous to a cloned D. melanogaster DNA segment, Dm 25, has been examined in polytene chromosomes by hybridization in situ. Dm 25 localizes to multiple sites and shows variation in patterns between different strains and among individuals within wild-type laboratory strains. Analysis of numerous geographically distinct isogenic lines suggests that Dm 25 patterns are determined by germ-line factors and are not the product of strictly somatic events. In general there is wide variation in Dm 25 patterns among different lines, but a significant number of sites are common to two or more distinct lines. Hybridization to restriction digests of genomic DNA suggests that Dm 25 is a moderately repetitive, conserved sequence whose copies are dispersed throughout the genome. Analysis of species other than melanogaster indicates a significant divergence in structure of sequences homologous to Dm 25 as well as a drastic reduction in amount of homology to the melanogaster sequence.