The rat and mouse Cyp2d locus. Expansion in the mouse leads to non-orthologous relationships between these genes. These rat genes have had official CYP names for more than 15 years; in fact, they were the first five genes in the Cyp2d subfamily to be identified. For more details on rat P450 nomenclature, see http://drnelson.utmem.edu/cytochromeP450.html. Abbreviation: bp, base pairs.