The complete three-billion base sequence of DNA, deoxyribonucleic acid, for any individual is unique, like no other human’s (except in the case of identical twins) (Browning 1). This single substance has recently been used as evidence in U.S. courtrooms. Many experts say “its [DNA] precision damns the guilty and frees the innocent” (Cheney 2). This nucleic acid’s precision develops a fingerprint, which identifies a criminal. The test to find such a fingerprint consists of two DNA samples-- one from the suspect’s blood or other body tissue and the other from the victim or crime scene. After certain tests find two sets of fingerprints, scientists look for a match between the two. If one is found, DNA exonerates the innocent and terrifies the guilty (Browning 1). Accurate, concluding genetic tests on DNA have served as great evidence to convict or free criminals throughout the judicial system.

Located in the nucleus of every cell in the body, DNA holds the basis of individuality, making the blueprint of a convicting genetic fingerprint (Froelich and Leyden 3). It consists of four chemical substances-- adenine, cytosine, thymine, and guanine (Browning 1). Adenine joins onl

y to thymine to form one pair of bases. Cytosine joins only to guanine to make another pair. These four bases fit between DNA’s two strands which form a double helix ladder (Froelich and Leyden 3). DNA’s four organic units are arranged in a complex and unique combination in every individual’s cells. Two percent of DNA consists of a human’s genetic code which can be in any sequence of the four bases (Schefter 6). For example, each person has 23 pairs of chromosomes with about six million base pairs which are in a certain order to identify one person (Froelich and Leyden 3). With such a uniqueness between individuals, the probability that two people have the same DNA ranges anywhere “from 1 in 50,000 to 1 in 5 million” (Hancock and Miller 64). According to Dan Gramer, director of laboratory operations with Cellmark Diagnostics in Frederick, Md., the possibility of two people sharing the same DNA fingerprint is “1 in 1,000,000,000,000,000- a million billions” (Froelich and Leyden 1).

With such great odds, DNA can be tested to find the genetic fingerprint of a person. DNA testing, or fingerprinting, is a difficult process that looks for differences among samples of the nucleic acid. DNA fingerprinting derived from the use of polymorphism in medicine, which are silent variations between the genomes of different people. DNA tests also work with sites in DNA that have different lengths because of their variable numbers of repeated units (VNTRs) (Housman 543). The VNTRs are where DNA goes into “the genetic equivalent of a computer programming loop” and copies itself repeatedly. This takes place at the end of each chromosome and/or in tons of other identifiable locations along “DNA’s six-foot length” (Schefter 2-3). This process results in a genetic fingerprint. A fingerprint comes from a purified DNA sample which has been made into billions of copies and identified by types found in that sample (Cheney 3). Genetic fingerprinting uses the complex technology of an electrical field to separate DNA pieces by length and radioactive material to create a mark on an X-ray film of and individual’s DNA fingerprint (Froelich and Leyden 3). Examining a DNA fingerprint, one expert commented, “They look like nothing so much as ink spots, but these marks are more than that: they are a genetic portrait, an immutable chemical signature” (Cheney 1).

One genetic test, the Polymerase Chain Reaction (PCR), uses speed and precision to make a DNA fingerprint. The test itself is a significant advancement in genetic technology because of its complex yet significant techniques. The PCR test looks at six different inherited traits, each controlled by a specific gene. Each gene has at least two alternative forms, called alleles. This makes twenty-one possible combinations of alleles. PCR analysis looks for

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