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. Author manuscript; available in PMC: 2011 Apr 1.
Published in final edited form as: Brain Res Brain Res Rev. 2004 Oct;46(2):204–215. doi: 10.1016/j.brainresrev.2004.07.003

Fig. 1.

Fig. 1

Molecular evolution of vertebrate opioid receptors. Phylogenetic dendrogram (tree) was generated using the neighbor-joining method. Numbers above internal branches represent the bootstrap value (percentage giving the same topology at that node with 1000 bootstrap runs). Numbers along branches are branch length. Scale bar shows length in proportional difference (e.g., 0.05 equals 5% difference or divergence in amino acid sequence). Prefixes refer to the animal species: h=human; r=rat; m=mouse; rp=R. pipiens (frog); and dr=D. rerio (fish). MOR is the mu opioid receptor, DOR is delta opioid receptor, and KOR is the kappa opioid receptor.