Genetic Factors Affecting Hybrid Male Sterility Leading to Speciation

The process whereby speciation occurs can come about through the evolution of barriers to gene flow. One of these barriers to gene flow can be an incompatibility, which leaves hybrids dead or sterile. Two theories underlie the work of this experiment, Haldane’s Rule and the large X effect. Haldane’s Rule is the observation that unisexual inviability or sterility among species’ hybrids is almost always found in the heterogametic sex. The large X effect is the observation that substitution of one species’ X-chromosome for another’s has a disproportionately large effect on hybrid fitness compared to similar substitution of an autosome. For Drosophila, the cause of the large X effect has been identified as density dependent for the number of sterility-inducing incompatibilities on the Xchromosome. In this project we are using Drosophila simulans and Drosophila mauritiana. We are using introgressed lines of flies that make use of physical markers that can be used to track the progress of genetic material throughout crosses. The visible markers that we are using affect eye color and express fluorescent protein, allowing us to determine the regions on the recombinant chromosomes that contain the factors leading to hybrid male sterility. Males that carry the recombinant X-chromosomes are sterile unless the sterility factors have been removed via recombination. Flies that are fertile will be genotyped using Real-Time PCR. Genetic mapping will then allow us to determine the location of the sterility-causing gene in question. At this time we have generated a number of recombinant genotypes and through the genotyping of these samples we have narrowed our candidate region. At the start of this project the region was approximately 300kb in length and we have shortened that segment of interest to 100kb. By shortening this segment we have narrowed our search area for this sterility-causing gene that is of interest to us