"We also suggest that mammalian enamel is distinct from fish enameloid," the researchers reported in this week's online edition of the Proceedings of the National Academy of Sciences. "The similar nature as a hard structural overlay on exoskeleton and teeth is because of convergent evolution." The researchers include Dr. Kazuhiko Kawasaki, senior research associate and Dr. Kenneth W. Weiss, the Evan Pugh Professor of biological anthropology and genetics, Penn State and Tohru Suzuki, professor of agricultural science, Tohoku University, Japan.
While similar structures and traits are often similar because they come from the same genetic basis, it is not unusual to have physical traits that look alike and serve the same purpose, developed from completely unrelated genes.
The genes responsible for bones, enamel, dentine, milk and saliva in most vertebrates belong to the same family; that is, they descend from a common ancestral gene, and for the most part, reside on the same chromosome. These genes are all responsible for calcium binding; whether it is the growth of bone on cartilage, tooth components like enamel and dentine, or production of calcium rich milk and saliva. However, all calcium-binding genes do not exist in all vertebrates.
"Birds have a gene to make hard egg shells, but they do not have genes for making tooth components," says Kawasaki. "Birds probably lost the enamel gene so long ago that there would be no trace of it."
The researchers have traced the development of these calcium-binding genes to a gene, SPARC, that existed before the split occurred between invertebrates and vertebrates during t
Contact: A'ndrea Elyse Messer