GENOMIC DISTRIBUTION OF P-ELEMENTS IN DROSOPHILA-WILLISTONI AND A SEARCH FOR THEIR RELATIONSHIP WITH CHROMOSOMAL INVERSIONS

According to the recent-invasion hypothesis, Drosophila melanogaster m ay have acquired its P elements in a fairly recent process of horizont al transmission between species, Drosophila willistoni has been identi fied as the potential donor species in that transfer process, A most r emarkable feature of D. willistoni is its extensive chromosomal polymo rphism due to inversions-the adaptiveness of which has been the subjec t of many classical studies on evolutionary genetics, In this article, we further extend the study of P elements in D, willistoni, focusing on the possible role they may play in the generation of chromosomal in versions, Our results may be summarized as follows, P-homologous seque nces were detected in South American populations of D, willistoni. In two of them, a recently collected wild population and an old laborator y stock, the P insertion sites were located in the polytene chromosome s, Several hybridization sites were mapped in all major chromosome arm s of the natural population, which was also chromosomally polymorphic; in the laboratory population, nearly devoid of inversions, hybridizat ion sites were found to be confined to the chromocenter. In the wild p opulation, 10 of the 24 P hybridized sites coincided with several inve rsions break points and another five sites located themselves very clo se to those points, The results are discussed within the context of ev olutionary hypotheses.