Could Saddam Hussein's Smell Lead U.S. to His Lair?

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Mice are excellent at detecting differences between individuals. Beauchamp and his colleagues demonstrated that a mouse could tell the difference between two other mice genetically similar except for one MHC gene out of the 30,000 total genes in the mouse genome.

Though humans perceive far less sensory information through smell than other mammals—they have only 300 olfactory receptors compared to the mouse's 1,000—they still respond to odor signals even if subconsciously, says Diego Restrepo, a neuroscientist at the University of Colorado Health Sciences Center in Denver, Colorado.

Work done by scientists at the University of Chicago in Illinois and published last year in the journal Nature Genetics revealed that women can smell some genetic differences between men. Women preferred scents of men with similar—but not identical—MHC genes to their own. Scents from men with almost identical or starkly different MHC genes were not as desirable.

Other studies have revealed that women can also identify their infants by smell alone.

Beauchamp and his colleagues have devised an experiment that uses lab mice to detect the chemical markers in urine. The scientists are training mice to distinguish different MHC genes in human urine via scent.

A chemical analysis of the urine may indicate which volatile compounds—essentially a chemical profile—relays the genetic information, said George Preti, the organic chemist conducting the analysis. Once the scientists identify them, they'll synthesize a mixture and test it on the smart mice.

The goal is to build a sensor—an electronic "nose" that, coupled with a database of odortypes, can tell one individual from another.

The smell signature also applies to health. Beauchamp's team at Monell discovered that mice, for example, can distinguish older and younger genetically identical mice. They also use odor to identify animals infected with the Mammary Tumor Virus before any signs of disease are present. In Cambridge, England, dogs are being tested for their ability to sniff out traces of human prostate cancer in urine samples. Beauchamp anticipates that many diseases may have chemical signatures that may provide early diagnoses.

An understanding of chemical signatures may enable all kinds of sleuths to make heretofore impossible identifications.

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