SSS 2010-11-22

（单词翻译）

This is Scientific American's 60-Second Science. I'm Cynthia Graber. This will just take a minute.
You've seen it on TV. Crime scene investigators¹ show up at what might be a murder scene. There are blood spatters—but no body. Who's the victim? Now, a new technique developed in the Netherlands might help real-world investigators establish the age of the victim using only blood. The research was published in the journal Current Biology. Usually, age is determined² by physical characteristics, such as teeth or bones. Great—if you have a body. Researchers have tried unsuccessfully to use blood. But in this study, the scientists used immune cells called T-cells. T-cells recognize invaders³ through receptors that match molecules⁵ on bacteria, viruses, even tumors. The cellular⁶ activity that produces these receptors also produces a type of circular DNA⁷ molecule⁴ as a by-product⁸.
The number of these receptor by-products declines regularly over time. So scientists devised a test to measure the molecules—and use that to infer someone's age based on his or her blood. The results appear to be accurate to within plus or minus nine years. So forensic⁹ scientists could use a bloodstain to narrow a victim's age to within two decades. That's a big range—but it could help solve crimes when the victims can't be found.
Thanks for the minute. For Scientific American's 60-Second Science, I'm Cynthia Graber.