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Restriction enzymes are like chemical scissors. They are capable of cutting DNA into fragments at sites called restriction sites. The DNA fragments are then separated by gel electrophoresis. In this instance, DNA is placed into a gel called agarose and an electric current is run through it. Because DNA is slightly negatively charged, the fragments migrate through the gel toward the positive pole. Smaller fragments of DNA travel through the gel farther and a banding pattern is the result. Because the DNA was treated with a primer, when an Xray is made of the DNA fingerprint, the banding pattern will be displayed on the film. Each person's unique DNA produces a banding pattern all their own. In forensics, if someone leaves behind DNA evidence, and suspects are investigated, the DNA fingerprints can be used to identify whose DNA was actually at a crime scene. Restriction enzymes can be used in the field of forensics to distinguish genes by recognizing single base changes in the DNA. These are called single nucleotide polymorphisms or SNP's. If a restriction site is altered due to the presence of an SNP, the altered restriction sites will not be cut by the restriction enzyme leaving a single band of DNA. Those genes with correct restriction sites will generate two visible bands of DNA on the gel. Therefore, the number of bands reveals much about a person's genotype. Watch the simulation of DNA fingerprinting at the link below. It is easy to understand and informative.
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