This figure shows the routes to ortholog assignment. Reciprocal Best Hit (RBH), labelled route 1, conveys if two genes in carp and human find each other as the best hit in the other species. Stepped Reciprocal Best Hit, SRBH (route 2), extends RBH by using a closely related species, zebrafish, to enhance ortholog assignments. This is possible as the zebrafish has many more sequences in the databases, its genome is significantly more annotated and it has a genome sequence available. The Conditional Stepped Reciprocal Best Hit combines both RBH and SRBH as some sequences are still missing from zebrafish.