In our laboratory we seek to understand the molecular mechanisms responsible for speciation (i.e., the process by which barriers to gene flow evolve between populations). Today we know that these mechanisms often involve incompatibilities among genetic variants that function normally in their usual genetic background and produce perfectly fit individuals but generate sterility and/or inviability when encounter variants from other species in inter-specific hybrids. Our approaches use methodologies that combine classic genetics, modern genomics and population genetics, and multiple closely related species of fruit flies that hybridize in nature. Research projects include: (1) the characterization of landscapes of natural introgression (i.e., genetic exchange through species hybridization in their natural environment), (2) the genetic basis of hybrid female sterility, and (3) the molecular and gene regulatory basis of the disproportionate effect of the X chromosome on hybrid male sterility. More recently, and in collaboration with Dr. Comeron, we reported for the first time the presence of an active meiotic drive mechanism for the X chromosome, which results in the preferential inclusion in oocytes of chromatids with crossovers. We are currently attempting to elucidate its molecular causes.