The evolution of reproductive barriers is essential for speciation - the process by which one species splits into two. One of the fastest barriers to evolve between species is the sterility of hybrid males. With a speciation event of 175,000 years ago, the USA and Bogota subspecies of the fruit fly Drosophila pseudoobscura are among the youngest pair of species to be studied genetically. Crosses between Bogota females and USA males results in sterile hybrid males. Rarely, these hybrid males are able to produce offspring, but when they are successful all offspring are female, a process known as sex-ratio distortion. The hybrid incompatibility system of Drosophila pseudoobscura is the premier system to study the role of selfish genetic elements such as segregation distortion in the evolution of new species. The genetic architecture underlying both sterility and segregation distortion in this system is complex. One of these components has been identified so far - Overdrive (Ovd), located on the X chromosome of Bogota is required for both sterility and distortion. Ovd, however, has no effect on its own and requires an interaction with a dominant autosomal gene. Previous mapping suggests that this gene, whose interaction with Ovd is essential for both hybrid phenomena, is located on the second chromosome of USA. My goal is to identify this autosomal factor using an approach that combines an X-ray mutagenesis screen with whole genome sequencing. Identification of this final component of the Drosophila pseudoobscura hybrid incompatibility system will provide key information on the genes underlying segregation distorters and hybrid sterility between species, and open the door to understanding molecular mechanisms of selfish genes.