Abstract
A follow-up over 83 generations has been carried out, by the Southern blotting technique, of a Drosophila stock which is unstable in the location of Bari 1 elements. The persistent intrastock polymorphism detected is largely amenable to insertion/excision equilibria at 36 genomic sites that form a gradient in occupancy. In a closely related stock, Bari 1 elements are stable and exhibit a substantially different genomic distribution. These results suggest that in Drosophila preferential insertion sites may be defined with the contribution of host factors, although alternative interpretations are also possible. The relevance to the mechanism(s) that contains the potentially deleterious effects of transposition is discussed.
