| October 24, 1996 | . | Vol. 26 No. 10 |
Unisex haircuts and clothing can sometimes make gender identification difficult, but once the clothes come off, identification is easy. Forensics specialists and archaeologists have not had such an easy time when uncovering human skeletal remains, especially those of young children, but researchers may have a DNA solution to the problem.
Some methods of determining gender from DNA studies of the X and Y chromosomes -- the so called sex chromosomes -- have been developed, but are inappropriate for use in archaeological situations where the genetic material is old and only short segments of DNA can be replicated using current laboratory methods. Some existing methods use gene sequences that are only on the Y, or male chromosome. The presence of that sequence indicates that the subject was male, but the absence does not prove that the subject was female.
The researchers, including Stone, George R. Milner, professor of anthropology, Mark Stoneking, associate professor of anthropology, and Svante Paabo of the University of Munich, worked with the amelogenin gene.
"The interesting thing about this small part of the amelogenin gene is that, while it occurs on both the X and Y chromosome, there are fixed differences between the male and female version," Stone said.
Stone looked at DNA samples from 20 adult skeletons. These individuals could be definitively sexed using their cranial and pelvic bone features. She also looked at modern DNA samples taken from blood.
While anthropologists and forensics experts have been determining sex by examining known skeletal differences between men and women for years, this technique will not work for juveniles. The differences that occur between men and women only become apparent after puberty. Experts sometimes also have difficulty definitively deciding on the sex of a skeleton if it falls in the area where the male and female ranges overlap or if only fragments are recovered.
Stone extracted DNA from the modern blood and the ancient bones and, using a process called polymerase chain reaction, isolated the amelogenin segments of the DNA. These isolated segments were then replicated again to increase the amount of DNA available.
The amplified DNA was then tested to determine which form of the amelogenin gene each contained.
"The blind typing of the modern DNA produced 19 correct sex identifications and one that came up female when the sample was labeled male," Stone said. "A second DNA-based sex typing method was used on the one incorrect sample and it too produced a female result. It appears that this sample was mislabeled in the field and the new method correctly identifies this person's sex."
For the ancient samples, one individual was DNA typed as female when the skeletal examination indicated the he was male. This individual's DNA was extremely difficult to extract and the amount was probably insufficient to produce a reliable result. The other individuals were all correctly identified.
There are other DNA tests that can determine sex in living populations when large quantities of DNA can be obtained. However, this method appears to be more sensitive than other DNA methods to very low quantities of DNA, Stone said.
Extracting DNA from ancient or badly preserved bones can be difficult. A method that uses only a minute amount of DNA but reliably produces correct sex types can help in archaeological research and in identification of victims in forensic settings.
"Until recently, the size and shape of bones were the only means of establishing the sex of skeletons from archaeological or forensic contexts," Anne C. Stone, graduate student in anthropology, said. "The ability to recover DNA from bone opens the way for determining sex in cases of juvenile remains or where only bone fragments are recovered."
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