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DNA Fingerprinting in Forensic Science

Learn about DNA profiling, its accuracy in criminal cases, chromosome structures, polymorphisms, DNA collection, avoiding contamination, DNA sample preparation, and applications in forensic investigations.

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DNA Fingerprinting in Forensic Science

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  1. Chapter 7 DNA Fingerprinting Forensic Science: Fundamentals & Investigations, Chapter 7

  2. Introduction and History of Biological Evidence in Forensics • DNA fingerprinting, also known as DNA profiling, is used in criminal or legal cases with a high degree of accuracy. • Biological evidence such as blood, saliva, urine, and the roots from hair is examined for the presence of inherited traits. Forensic Science: Fundamentals & Investigations, Chapter 7

  3. The Function and Structure of DNA • DNA molecules make up chromosome structures and are found in the nucleus of cells in the human body.

  4. DNA Identification • Junk DNA contains many of the unique patterns of repeated base sequences that identify individuals. • In a human population, these are called polymorphisms.

  5. Sources of DNA • A perpetrator may leave biological evidence, such as saliva or blood, at a crime scene. • This individualized evidence is capable of identifying a specific person. • In 1993, the polymerase chain reaction (PCR) technique was invented. It generates multiple copies of DNA evidence. • The DNA is then viewed using the process of gel electrophoresis. Forensic Science: Fundamentals & Investigations, Chapter 7

  6. Avoiding contamination in the collection and preservation of DNA • Use disposable gloves and collection instruments. • Avoid physical contact, talking, sneezing, and coughing in the evidence area. • Air-dry evidence and put it into new paper bags or envelopes. • If evidence cannot be dried, freeze it. • Keep evidence cool and dry during transportation and storage. Forensic Science: Fundamentals & Investigations, Chapter 7

  7. Preparing DNA Samples for Fingerprinting • DNA is mixed with special enzymes. • The enzymes cut apart the DNA in specific places forming different sized fragments. • The DNA is loaded into the chambers found on an agarose gel. • An electric current is passed through the gel separating the fragments by size. • ***More detail on this process given in another notes handout.

  8. Analysis of DNA Fingerprints and Applications • Bands and widths are significant in matching samples of DNA. • DNA fingerprinting can (a) match crime scene DNA with a suspect, (b) determine maternity, paternity, or match to another relative, (c) eliminate a suspect, (d) free a falsely imprisoned individual, and (e) identify human remains. Forensic Science: Fundamentals & Investigations, Chapter 7

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