Phylogenetic tree of Adhesion , Frizzled , Secretin and Glutamate families. The trees were calculated using the neighbour-joining method with 1000 bootstrap replicas. The one-to-one orthologous pairs are represented in red. (A) The Adhesion receptor family. I-VIII represent the different groups of the Adhesion family. (B) The Frizzled receptor family. (C) The Secretin receptor family. (D) The Glutamate receptor family.