Analysis of OR families by phylogenetic comparison. OR sequences used to construct the phylogenetic trees correspond to the dog and rat sequences retrieved in this work or taken from  (human) and  (mouse). (a) Magnification corresponding to a part of family 2, including subfamilies E to G and I to K (general combined phylogenetic tree as provided in Additional data files 4 to 20). Circled letters identify dog and rat subfamilies. (b) Rat, dog and mouse subfamilies 2I and 2K (the corresponding subfamilies do not exist in humans). Rat genes are in red, dog genes in blue and mouse genes in green. (c) Subfamilies 6AL and 6B (note that subfamily 6AL is present in rat and dog repertoires but is absent from the human and mouse repertoires and that subfamily 6B is present only in the dog repertoire). The color code is the same as in (b).