Police are hoping that DNA fingerprinting will help bring them one step closer to identifying a suspect in the Venable area rape case that shook the University community last month.
DNA evidence from the crime scene is being compared to DNA profiles from all of the databanks in the United States.
"So far we've had no luck," Charlottesville Police Sgt. Ralph Barfield said, "but we're going to keep trying."
DNA fingerprinting, also called DNA typing, was first introduced into U.S. courts in 1988. At the time the technology was hailed as the most significant forensic advance since classical fingerprinting.
It relies on the fact that every person's DNA is made up of a unique sequence of chemical bases called nucleotides. There are four types of these chemical building blocks: adenine, thymine, cytosine and guanine. They are arranged into two connected strands that spiral around each other in a series of pairs, giving DNA its double helix shape (see information box below).
The order in which the base pairs are arranged in the DNA strands determines what types of genes the DNA will form. Since genes determine physical traits, this order determines everything from height to eye color.
Since no two people have exactly the same sequence of building blocks in their DNA, an individual can be identified by the order of these base pairs.
"Basically what you can do is take DNA and chop it up into pieces using things called enzymes," Biology Prof. Reginald H. Garrett said. "There are these regions in the human chromosome that don't have important information and because of that they are highly variable."
It is easy to separate these DNA fragments, and all people have a fingerprint of these pieces, Garrett explained. By examining the patterns of fragment sizes, scientists can identify specific individuals.
This profile cannot be matched to another profile with 100 percent accuracy. But Garrett estimates that genetic fingerprinting can isolate one suspect out of a group of 10 billion people.
DNA typing begins when police gather physical evidence from a crime scene, Barfield said. In the case of a rape, this is often seminal or vaginal fluid. Hair, saliva or any other kind of genetic material will also work. These samples are sent to a forensic lab to be analyzed.
After the forensic lab obtains a DNA profile from the various objects collected at the crime scene, the police can compare this to the DNA profiles of any suspects in the case.
If there are no suspects, or if the suspects' profiles do not match the lab profile, the profile is then compared to the Virginia DNA Databank. This databank includes the DNA profiles of over 90,000 convicted felons from the Commonwealth of Virginia. According to Barfield, this makes it "the second-largest DNA databank in the world - second only to Great Britain."
Sometimes, DNA from a crime scene matches the DNA of a previously convicted felon. In fact, the Virginia databank has averaged one to two blind hits per week, according to Barfield.
The DNA obtained from last month's Venable area rape scene has not produced one of these blind hits. Police have, however, been able to eliminate several suspects because of the DNA evidence, Barfield said.
(Cavalier Daily Associate Editor Lisa Ann Kaufman contributed to this story.)
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