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Just as everyone has their own fingerprint, everyone also has their own
DNA patterns. DNA testing, also known as DNA profiling and
genetic fingerprinting, allows those patterns to be uncovered.
Today DNA testing plays a big part in forensic genetics and is often used
to confirm that a person was present at a certain location, determine
identity, and assign paternity.
Each person has roughly 3 billion base pairs of DNA, but most people don't know that 99.999% of DNA is exactly the same in one person as it is in another. So how do scientists identify humans via DNA? The process involves looking at so-called "junk DNA," extra DNA that all humans have, that doesn't seem to serve any purpose. Scientists have found that short stretches of junk DNA vary between individuals. Short tandem repeats are sections of DNA arranged in back-to-back repetitions. The number of repeats varies from one person to another. The variations are called alleles. Scientists use alleles to distinguish one person from another, as the possibility of people having identical alleles is slim to none.
Biological evidence is anything that was once living, such as blood, saliva, semen, and hair. Blood is the best evidence because of the sheer number of cells it contains, but even one tiny skin cell has enough evidence to make a fingerprint.
At the lab, the DNA is first extracted from the samples. Once isolated, it is analyzed in a process called polymerase chain reaction, or PCR. The PCR process enables many copies of specific parts of the DNA molecule to be made.
In the United States, 13 standard markers are used for matching human samples, plus one additional marker to determine gender. The technology used today in DNA testing allows it to be done very quickly; in most cases, it takes less than 24 hours to get one genetic fingerprint.
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The DNA Testing Process