Abstract
Distribution spectra of mdg1, Dm412, copia, and B104 in a descending series of isogenic scute lines of Drosophila melanogaster were analyzed. Transpositions of mobile elements occurring during isogenization were shown to be the main source of insertion site polymorphism detected in daughter lines. Isogenization resulted in a significant increase in transposition frequency (approximately approximately 10(-2) per site per genome per generation).