How to Do DNA Forensics
DNA forensics is a group of techniques that attempt to identify the individual that a DNA sample belongs to. It's commonly used to determine criminal suspects, and similar techniques also are used to establish paternity. DNA forensics relies on specific locations in the chromosome, rather than the entire genome. These procedures vary considerably in the specifics, but they consist of the same general steps.
Instructions
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Obtain the DNA samples. The test sample can be almost any human tissue, but is most often blood, hair follicles, saliva or semen. The reference sample from the test individual is typically blood or saliva.
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Digest the DNA with an enzyme. A restriction endonuclease is a type of enzyme that splits a double strand of DNA at a specific DNA sequence.
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Separate the resulting DNA fragments with gel electrophoresis. This process uses a positive electrode to drag the negatively charged DNA fragment through a gel. The smaller fragments experience less drag than the larger fragments and therefore move more rapidly through the gel. This produces a separation of the DNA fragments by size.
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Denature the separated DNA fragments by soaking it in a base. Blot the gel with a nylon membrane to maintain the spatial arrangement of the fragments. This part of the procedure is called a "Southern blot."
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Hybridize the DNA fragments with a radioactive label. Subject the DNA to specific conditions of salt and temperature that will cause complementary strands of DNA to join together. Choose radioactive labels that will attach to specific loci on a human chromosome. Take an X-ray of the labeled DNA fragments and analyze the DNA profile of the sample.
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