Evolutionary origin of secreted and transmembrane domain proteins. Proteins in the ‘nematode’ group have no homologs outside the nematodes. The ‘metazoan’ group consists of proteins with homologs in invertebrate and vertebrates, but not in plants or fungi. The ‘eukaryotic’ group contains proteins with homologs in all the above groups. The ‘unclassified” group contain proteins that could not be grouped (see Materials and Methods for details).