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Ward's World+MGH Forensic Biology

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5 Forensic Biology: Test Your Understanding Teacher's Guide + ward ' s science 1. How does a forensic biologist use a DNA profile to link victims and suspects with a crime scene or exclude a suspect from association with a crime? A forensic biologist will compare the DNA profile from a crime scene known samples, from a database, such as the Combined DNA Index System, or CODIS. 2. How is DNA amplification different from DNA quantification? DNA quantification allows biologists to determine the concentration and purity of DNA in a sample. DNA amplification refers to a region of DNA where biologists make a single copy or copies of segmented DNA. 3. What is the difference between organic and solid-phase extraction? During organic extraction, cells undergo lysis with the help of a detergent buffer to extract DNA. Next, an organic phase separation technique purifies the extracted DNA. Lastly, centrifugation concentrates the extracted DNA. This process is different from a solid-phase extraction in which a solid membrane captures the extracted DNA sample. Several washes help remove impurities from this sample. 4. Critical Thinking: A forensic biologist is working to help solve a missing-person case. A recent break in the case involves the identification of a badly decomposed body. The biologist uses a forensic mitochondrial DNA (mtDNA) marker to identify whether this decomposed body is related to the missing-person case. Why would she choose this particular genetic marker? Sample answer: One reason the biologist would use mtDNA is because the body might be so badly decomposed that there is very little to sample. mtDNA exists in high copy numbers in each cell, and therefore has a better chance of being detected in small samples. The use of mtDNA is also appropriate as it can be typed from degraded DNA. 5. Critical Thinking: Assume the role of a forensic biologist at a crime scene. What four steps would you take to determine the DNA profile of a suspect's blood sample? The first step I would take is to extract DNA from the sample. Next, I would assess the quantity and quality of the DNA sample. Third, I would amplify the genetic markers in this sample using PCR. Then I would separate and detect the amplified products to determine the suspect's DNA profile. 5

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