Tooth enamel protein can show sex of human remains

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A new method for estimating the biological sex of human remains based on reading protein sequences rather than DNA has been used to study an archaeological site in Northern California.

The protein-based technique gave superior results to DNA analysis in studying 55 sets of human remains between 300 and 2,300 years old. The work is published in Scientific Reports.

The researchers compared three methods for sex determination: the new proteomic method; DNA analysis; and osteology, or analysis of the size, shape and composition of the bones themselves. They applied these methods to remains from two ancestral Ohlone villages near Sunol, California. The site is being excavated by the Far West Anthropological Research Group of Davis in collaboration with the Muwekma Ohlone tribe.

Amelogenin is a protein found in tooth enamel, the hardest and most durable substance in the human body. The gene for amelogenin happens to be located on both the X and Y sex chromosomes, and the amelogenin-Y protein is slightly different from amelogenin-X.

The method works by retrieving a tiny amount of protein from a tooth. All proteins are made up of a chain of amino acids, so the protein is analyzed to give the amino acid sequence, which then defines the protein. Each of the 20 naturally occurring amino acids is specified by a three-letter code in DNA, so it is possible to work backward from the amino acid sequence and figure out the likely DNA code.

The researchers were able to determine the sex of all of the remains using the new protein method and all but five using DNA methods. Results from osteology and proteomics agreed in almost all cases, although examining bones themselves was only effective for about half the skeletons.

The protein method allowed them to estimate sex for children, which is not possible from osteology. It was reliable even when the signal from DNA was weak.

Being able to determine the biological sex of human remains provides a greater window into the persona of each individual. Anthropologists are interested in determining biological sex because sex interacts with health and can have a large impact on how people form an identity and are treated within a society.

“Almost every human society around the world incorporates sex and gender as a way to classify people, and these can affect your status and who you associate with in society,” Eerkens said.

Research article: A comparison of proteomic, genomic, and osteological methods of archaeological sex estimation

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