Analysis of a Strong Suppressor of Segregation Distorter in .

() is a naturally occurring male meiotic drive system in , characterized by almost exclusive transmission of the chromosome owing to dysfunction of sperm receiving the homolog. Previous studies identified at least three closely linked loci on chromosome required for distortion: , the primary distorting gene; (), which increases the strength of distortion; and (), the apparent target of Strength of distortion is also influenced by linked upward modifiers including () and (), and by various unlinked suppressors. Although is known to encode a mutant RanGAP protein, none of the modifiers have been molecularly identified. This work focuses on the genetic and cytological characterization of a strong -linked suppressor, , capable of restoring Mendelian transmission in males. and its cohort of positive modifiers appear to act semiquantitatively in opposition to with distortion strength depending primarily on the total number of distorting elements rather than which particular elements are present. can also suppress male sterility observed in certain genotypes. To facilitate its eventual molecular identification, was localized by deletion mapping to polytene region These studies highlight the polygenic nature of distortion and its dependence on a constellation of positive and negative modifiers, provide insight into the stability of Mendelian transmission in natural populations even when a drive system arises, and pave the way for molecular characterization of whose identity should reveal new information about the mechanism of distortion.