Abstract
Multicopied DNA sequences with homology to the complete 2.9kb P element from a P strain in the USA were detected in nine natural strains (two P strains, three Q strains, four M strains) of Drosophila melanogaste from Japan and one (M strain) from Korea. Southern hybridization patterns with pπ25.1, which contains the complete P element, showed highly polymorphic distribution of P elements in genomic DNAs from these strains. Nevertheless, all these natural strains including strong M strains had a similar number i.e., about 50 copies of P elements per genome. However, the number of central-portion-retaining P elements surveyed by hybridization to PstI fragment from pπ25.1 was not similar in these strains; it was 25 for a fairly strong P strain, 16 for a weak P strain and 16-14 for two Q strains, but only 1 to 9 for five strains (Q, weak M, strong M) from a small island (Chichi Jima) and 8 for a weak M strain from Korea. The origin of these polymorphic P elements is discussed in relation to the hypothesis that they are descendants produced by mutational degradation from similar primordial P elements with P factor activity, which were created recently to a similar number per genome.
