If you want to know whether zebrafish have a gene similar to human Gene X, what should you do? One simple approach would be to use UniGene in the NCBI database (National Center for Biotechnology Information; http://www.ncbi.nlm.nih.gov/unigene), which provides lists of orthologs (functionally equivalent genes). This means that if you enter the name of a gene into UniGene, for example Gene X, you get orthologs found in various organisms. Of course, this search is limited to information on Gene X and its orthologs catalogued in UniGene. In recent years, the gene data in UniGene have been accumulating exponentially.