Analysis of a Strong Suppressor of Segregation Distorter inDrosophila melanogaster

R. G. Temin,  Genetics,  215:1085-1105. 2020.

Segregation Distorter(SD) is a naturally occurring male meiotic drive system inDrosophila melanogaster, characterized by almost exclusive transmission of theSDchromosome owing to dysfunction of sperm receiving theSD(+)homolog. Previous studies identified at least three closely linked loci on chromosome2required for distortion:Sd, the primary distorting gene;E(SD)(Enhancer of SD), which increases the strength of distortion; andRsp(Responder), the apparent target ofSd. Strength of distortion is also influenced by linked upward modifiers includingM(SD)(Modifier of SD) andSt(SD)(Stabilizer of SD), and by various unlinked suppressors. AlthoughSdis 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 strongX-linked suppressor,Su(SD), capable of restoring Mendelian transmission inSD/SD(+)males.Sdand its cohort of positive modifiers appear to act semiquantitatively in opposition toSu(SD)with distortion strength depending primarily on the total number of distorting elements rather than which particular elements are present.Su(SD)can also suppress male sterility observed in certainSDgenotypes. To facilitate its eventual molecular identification,Su(SD)was localized by deletion mapping to polytene region13C7-13E4. 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 ofSu(SD)whose identity should reveal new information about the mechanism of distortion.


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