Molecular mechanisms of meiotic drive

Segregation Distorter
Sex Ratio

The selfish Segregation Distorter complex of Drosophila melanogaster

Segregation Distorter (SD) is a well-studied selfish gene complex in D. melanogaster. In SD/SD+ heterozygous males, the SD chromosome is transmitted to 95% of the progeny by killing spermatids that have sensitive alleles of its target locus, Responder (Rsp)- a large satellite repeat near the centromere of chromosome 2. Despite knowing the molecular identity of both the distorter and the target, the mechanism behind distortion is unknown.

We use genomic, genetic, molecular and cytological approaches to study the mechanism behind segregation distortion and the effects of selfish genes on genome evolution and the genetic control of spermatogenesis. One hypothesis that we are testing is the possibility that small Rsp RNAs are affected by SD in the testis.

Modifiers of SD exist across the genome. Three enhancers of segregation distortion located on the 2nd chromosome ( E(SD), M(SD), and St(SD) ) are frequently held in linkage disequilibrium with the driver through inversions. Suppressors of segregation distortion on the 3rd ( Su(SD)3 ) and X ( Su(SD)X ) chromosomes segregate at high frequencies in natural populations. The molecular identities of these modifiers are currently unknown but discovering their identities promises to provide important insight into the mechanism behind segregation distortion. We are using genetic and association mapping methods to map the modifiers of SD.

Sex ratio meiotic drive and Y-linked resistance in Drosophila affinis

At least two sex ratio meiotic drivers segregate in Drosophila affinis populations. In collaboration with Drs. Rob Unckless and Andy Clark, we found Y-linked variation in the susceptibility to meiotic drive. In collaboration with Dr. Rob Unckless, we study these sex ratio systemsand the possibility that they contribute to the maintenance of Y chromosome morphological variation in D. affinis.
One example of a phenotype in the testes of Drosophila affinis sex ratio males: approximately half of the nuclei are not properly condensed in this cyst of elongating spermatids.