01 - Left at the Scene of the Crime: Intro to Forensic Science
reaction (PCR) and DNA fingerprinting a very small amount of DNA from a biological sample can be analyzed. In many cases the crime can only be solved, and the criminals brought to justice, through the meticulous work of forensic scientists. DETECTION OF BLOOD SPATTERS
Often trace amounts of blood cannot be detected by the naked eye, however it can easily be en- hanced and made visible by spraying the area with certain chemical enhancers such as Leucocrystal violet. This reagent will react with blood to generate a purple/violet color. In this experiment, students
will use Leucocrystal Violet to differentiate between trace blood samples and on different objects simulating materials recovered from a crime scene. DNA FINGERPRINTING In humans, DNA is packaged into 23 pairs of chromosomes that are inher- ited from an individual’s biological parents. Although most of this genetic material is identical in every person, small differences, or “polymorphisms”, in the DNA sequence occur throughout the genome. For example, the simplest difference is a Single Nucleotide Polymorphism (or SNP). Changes in the number and location of restriction enzyme sites result in Restriction Fragment Length Polymorphisms (or RFLPs). Short repetitive stretches of DNA at specific locations in the genome can vary in number to produce STRs (Short Tandem Repeats) and VNTRs (Variable Number of Tandem Re- peats). Although most polymorphisms occur in non-coding regions of DNA, those that disrupt a gene can result in disease. Medical diagnostic tests can identify specific polymorphisms associated with disease. Analyzing several different polymorphisms within a person’s genome gener - ates a unique DNA “fingerprint”. DNA fingerprints can allow us to distinguish one individual from another. Because polymorphisms are inherited, DNA fingerprints can also be used to determine paternity/maternity (and other familial relationships). The best-known application of DNA fingerprinting is in forensic science. DNA fingerprinting techniques are utilized to interpret blood, tissue, or fluid evidence collected at accidents and crime scenes. After DNA is extracted from these samples, forensic scientists can develop a DNA fingerprint. The DNA fingerprint from a crime scene can then be compared to the DNA fingerprints of different suspects. A match provides strong evidence that the suspect was present at the crime scene.
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