Figure 3
From: Conservation and co-option in developmental programmes: the importance of homology relationships
Evolution of the secretory calcium binding phosphoprotein (SCPP) gene family involving gene duplication and co-option. A duplication event of an ancestral SPARC gene (1) in the vertebrate lineage generated two paralogues (2), and one of these (SPARCL1) gave rise to the SCPP gene family through subsequent tandem gene duplications after the divergence of cartilaginous and bony fish (3). In mammals, the formation of tooth and bone tissue is based upon the presence of various members of the SCPP gene family, including genes for enamel SCPPs, dentin/bone SCPPs, as well as milk caseins and salivary proteins. Most of these are closely linked on one chromosome in humans, as shown in the diagram.