His group works on the identification of Y-linked genes and on the evolution of gene content of Y-chromosomes in a large number of Drosophila species. These genes are embedded within highly repetitive DNA, which creates many problems for genome sequencing and gene identification. A significant contribution of his group has been the development of computational methods to solve these problems, which resulted in the identification of nearly all known Drosophila Y-linked protein coding genes. These studies also shed light on the evolution of the Drosophila Y chromosome which, unexpectedly for a Y chromosome, is gaining genes, instead of losing them.