Kallikrein gene families have been identified previously in genomes of the 
human, the mouse, and the rat, and individual kallikrein-like genes have been 
found in many more species. This study presents the in silico identification of 
kallikrein gene families in the recently sequenced genomes of four additional 
mammalian species, the chimpanzee, the dog, the pig, and the opossum. 
Phylogenies were constructed with gene sequences from all seven mammalian 
families, using Bayesian analysis, which clarified the evolutionary 
relationships between these genes. Individual gene sequences, as well as 
concatenated constructs of multiple sequences, were used. Fifteen kallikrein 
genes were located in the chimpanzee (Pan troglodytes) genome, while only 14 
were identified in the canine (Canis familiaris) genome as no orthologue to 
human KLK3 was found. Thirteen genes were identified from the pig (Sus scrofa) 
genome, which lacked homologues to KLK2 and KLK3, and 11 genes, orthologous to 
human KLK5 through KLK15, were found in the opossum (Monodelphis domestica) 
genome. No kallikrein genes were identified from the available genome sequences 
of the chicken (Gallus gallus) or African clawed frog (Xenopus tropicalis). 
Within the family of kallikreins several subfamilies were suggested by 
phylogenetic analysis. One consisted of KLK4, KLK5, and KLK14; another of KLK9, 
KLK11, and KLK15; a third of KLK10 and KLK12; a fourth of KLK6 and KLK13; and 
finally one of KLK8 and the classical kallikreins (KLK1, KLK2, and KLK3).