Deletion of pepsinogen-coding genes in the platypus genome. (a) Synteny map of the loci containing PGB and PGC in vertebrates shows a strong conservation of the genes encoding pepsinogen C and its flanking genes, with the exception of platypus, in which PGC has specifically been deleted. The figure also shows how the gene encoding pepsinogen B appeared in therians as a result of a duplication of PGC to a nearby locus, followed by a translocation. The corresponding region in the platypus genome lacks any pepsinogen-coding gene. Functional pepsinogen genes are colored in blue, whereas pepsinogen pseudogenes are in red. For human and dog, which underwent a translocation of the PGB locus, chromosomes are indicated on the left. The genome sequences analyzed are from platypus (Ornithorhynchus anatinus), human (Homo sapiens), dog (Canis familiaris), opossum (Monodelphis domestica), lizard (Anolis carolinensis), chicken (Gallus gallus), and frog (Xenopus tropicalis). (b) Synteny map of the PGA locus in different vertebrate species shows the deletion of this gastric protease gene in the platypus genome. Bacterial artificial chromosomes (BACs) and fosmids used in the study are indicated at the top of each panel. Gene colors and scale are the same as in panel a.