Investigators have asked the families of people missing in Tuesday's attack on the World Trade Center to bring in toothbrushes and hairbrushes that may contain DNA to help identify bodies and body parts found in the rubble.
Rescuers are still going through an estimated 457,000 tonnes of debris from the 110-story twin towers and other structures destroyed or damaged on Tuesday when two hijacked airplanes slammed into the complex, possibly killing thousands.
Nearly 5,000 people are still missing. Of 159 bodies received, only 99 have been identified. Fifteen of the identities were established by examining partial remains.
Investigators often use jewelry, dental work or even clothing to identify crash victims.
With rescuers sometimes finding just fragments of human bodies, they hope that advanced technology will allow them to identify the missing using DNA gleaned from hair from combs or razors.
Where possible, children and parents of those feared killed are also being encouraged to provide DNA samples to help identify the remains.
New York's chief medical examiner, Charles Hirsch, said police would manage the collection of personal items like toothbrushes and underwear and also swabs from the inside of relatives' mouths to identify victims by their DNA.
"It will be the most likely identification means in this disaster," Hirsch said.
Any type of organism can be identified by examination of DNA sequences unique to that species.
Testing of DNA, which contains a person's genetic material, has become far more sophisticated in recent years. It is rapidly becoming the primary method for identifying and distinguishing among individual human beings.
Like the fingerprints that came into use by detectives and police labs during the 1930s, each person has a unique DNA profile, or what is sometimes called a DNA "fingerprint."
Unlike a conventional fingerprint that occurs only on the fingertips and can be altered by surgery, a DNA fingerprint is the same for every cell, tissue and organ of a person.
DNA fingerprinting is a laboratory procedure that requires several steps, including recovery of DNA from the cells or tissues of the body. Only a small amount of tissue -- like blood, hair, or skin -- is needed. For example, the amount of DNA found at the root of one hair is usually sufficient.
DNA fingerprinting has also been used in criminal cases, with a match of a suspect's DNA with DNA from a crime scene being used to convict suspects. It has also been used to clear the innocent.
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