Dr. Orr is an evolutionary geneticist with several broad interests. Most of his research focuses on the genetics of speciation and the genetics of adaptation. In particular, he is interested in the genetic basis of hybrid sterility and inviability, e.g., how many genes cause reproductive isolation between species? What are the normal functions of these genes and what evolutionary forces drove their divergence? He studies these problems through genetic analysis of reproductive isolation between species of Drosophila.
In his adaptation work, Dr. Orr is interested in theoretical rules or patterns that might characterize the population genetics of adaptation. He studies these patterns using both population genetic theory and experiment.
Genetic basis of male sterility in hybrids of Drosophila pseudoobscura and D. persimilis.
The strength of prezygotic (sexual) isolation plotted against genetic distance (D) among allopatric vs. sympatric species of Drosophila.