Fig. 2.

Phylogeny of intact V1R genes: 8 in dogs, 32 in cows, 4 in humans, 102 in rats, and 187 in mice. Shaded regions group the genes into 18 placental mammalian V1R families previously described in refs. 8, 10, and 12 or described here (see Results), with the family names indicated. Black circles mark family groups that contain more than one family as shown in Table 1. Dog branches are in red, cow branches are in black, human branches are in blue, mouse branches are in purple, and rat branches are in green. Bootstrap percentages supporting the family groups are shown if >50. The tree was reconstructed by using the neighbor-joining method with Poisson-corrected protein distances. The arrow points to where the tree is rooted with putative V1Rs of the frog Xenopus tropicalis (W.E.G. and J.Z., unpublished data). (Scale bar: 0.2 amino acid substitutions per site.)