Phylogenetic tree of prolactin and placental-prolactin family of sheep, cattle and goat. The tree was constructed using TreeView following the alignment of protein sequences given by the Clustal W 1.83 algorithm. The numbers at the base of each branch division represent bootstrap values after 10,000 repeats. The scale bar represents 0.1 amino acid replacements per amino acid site. For GenBank/DDBJ accession numbers, refer to Materials and Methods. The proteins in light blue areas were used for the multiple alignments in Fig. 3.