The fitness consequences ofPelement insertion inDrosophila melanogaster

Abstract

SummaryIn this study we estimate the frequency at whichP-element insertion events, as identified byin situhybridization, generate lethal and mild viability mutations. The frequency of lethal mutations generated per insertion event was 0·004. Viability dropped an average of 1% per insertion event. Our results indicate that it is deletions and rearrangements resulting from the mobilization ofPelements already in place and not the insertionsper sethat cause the drastic effects on viability and fitness observed in most studies of P–M dysgenesis-derived mutations. Elements of five other families (I, copia,412,B104, andgypsy) were not mobilized in these crosses. Finally, we contrast the density ofPelements on theXchromosome with the density on the four autosomal arms in a collection of thirty genomes from an African population. The relative number ofPelements on theXchromosome is too high to be explained by either a hemizygous selection or a neutrality model. The possible reasons for the failure to detect selection are discussed.