THE RELATIONSHIP BETWEEN STRUCTURAL VARIATION AND DYSGENIC PROPERTIESOF P ELEMENTS IN LONG-ESTABLISHED P-TRANSFORMED LINES OF DROSOPHILA-SIMULANS

Ten lines of Drosophila simulans were investigated with respect to P a ctivity, P susceptibility and the number and structure of their P copi es, eight years after transformation with the P element. All 10 were f ound to have reached a steady state. They exhibited varying levels of P activity (from 0 per cent to 96 per cent GD sterility) and, with the exception of one line, were not P-susceptible. In contrast with P ele ment behaviour in D. melanogaster. (i) no relationship was found betwe en the molecular pattern of P copies in a line and its ability to indu ce or to repress P expression in D. simulans; (ii) peculiar P element derivatives were observed in this species; (iii) the average number of P copies per genome was only half of that in D. melanogaster. This ma y result from transposon-host genome interactions, which lead to a low invading power of the P element in D. simulans.