Dec. 13, 2001 When researchers sought to learn whether President Thomas Jefferson had a child with a slave, they used a “Y chromosome test” that showed the boy was fathered by someone from the President’s family. Such tests indicate both the presence of male DNA in a blood or tissue sample—only males have Y chromosomes—and the family it came from, because the markers (particular chemical sequences) identified in the test are inherited.
Such tests were not used widely in the past because of a number of uncertainties. But usage is expected to increase now that the National Institute of Standards and Technology’s Chemical Science and Technology Laboratory has developed a more detailed and reliable method and, in turn, is creating a Standard Reference Material that labs will use to calibrate their instruments and validate test performance. The new test identifies 20 markers on the Y chromosome instead of the six used in older tests; the standard is expected to be ready for sale next year.
The new NIST methodology and SRM are expected to help simplify paternity testing as well as eliminate current problems distinguishing between male and female DNA in forensic and human ID tests.
The markers used in the test are short, brief chemical sequences repeated in pairs—often many times—in a DNA molecule. They vary enough in a population to distinguish individuals and produce good analytical results. None of the markers are believed to occur on X chromosomes, carried by both males and females.
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