Researchers at the University of California, Davis, have developed a technique that uses sensitive mass spectrometry for estimating the biological sex of human skeletal remains by measuring protein traces from teeth.
While researchers can measure features of bones such as the pelvis that differ between males and females, the skeletons of children and adolescents don’t show these structural changes. Also, sites may only yield a few pieces of bone. Plus, DNA analysis can be expensive, and DNA is fragile compared to other molecules.
Teeth, however, preserve well and are often found at archaeological sites, said UC Davis anthropologist Jelmer Eerkens, MA, PhD. Teeth also can tell researchers a lot about the person they belonged to, Eerkens added.
“Wear patterns on the tooth can tell us about diet. Morphology of the tooth can tell us about ancestry. (Different populations around the world have slight variations in the shape of teeth.) Plaque adhering to the tooth can tell us about bacteria in the person’s mouth, including pathogenic bacteria,” said Eerkens.
“We can radiocarbon ate the tooth to learn how old it is. And, stable isotope data can tell us about how a person travelled across the landscape,” Eerkens said.
The new method was developed by Glendon Parker, PhD, associate adjunct professor of environmental toxicology; Julia Yip, MS, a student in the graduate program in forensic sciences; and Brett Phinney, PhD, of the Proteomics Core Facility.
Amelogenin proteins play a role in the formation of tooth enamel. The genes for amelogenins are located on the X and Y chromosomes that determine biological sex in humans, though amelogenin has nothing to do with sex.
Forensic DNA analyses for sex often depend on looking for the amelogenin X or Y genes. Females will have amelogenin-X in their teeth. Males should have both the X and Y versions of the protein.
Yip looked at 40 enamel samples from 25 individuals including both adult and primary teeth from children. The teeth varied from 100 to 7,300 years old, collected from archaeological sites in North America and Peru.
Yip also examined samples from modern teeth. She was able to find traces of amelogenin-X in all the samples and amelogenin-Y in about half of them. A positive result for amelogenin-Y means the tooth must have come from an XY male.
Amelogenin-Y is usually at lower levels of amelogenin-X, so a tooth that tested negative for amelogenin-Y could be a false negative if there was just too little of the Y form to detect. To overcome this, the researchers developed a statistical method to work out the probability of such false negatives given a certain amount of amelogenin-X.
The new method adds another piece of to the information archaeologists can learn from a single tooth, Eerkens said.
“Like DNA, our method is quantitative and does not depend on anatomical training. It is cheaper to run per sample (than DNA) and can be done in non-sterile conditions,” Parker said, adding that the method likely would be used alongside existing techniques.
The study, “Sex Estimation Using Sexually Dimorphic Amelogenin Protein Fragments in Human Enamel,” was published by the Journal of Archaeological Science.