An orphan gene is essential for efficient sperm entry into eggs in .

Unlabelled: While spermatogenesis has been extensively characterized in the model system, very little is known about the genes required for fly sperm entry into eggs. We identified a lineage-specific gene, which we named ( ), that is required for efficient fertilization. Males that do not express produce and transfer sperm that are stored normally in females, but sperm from these males enter eggs with severely reduced efficiency.