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Spring 2011 What is DNA Fingerprinting? Objectives: Understand how DNA fingerprinting can be used in criminal investigations Describe the process of DNA fingerprinting Learn which part of the DNA genome is used for DNA fingerprinting Understand the factors that can increase the accuracy of DNA fingerprinting Interpret DNA fingerprints Explore various uses for DNA fingerprinting Recognize the limitations of and problems with DNA testing What Is Going to Happen: 1. Pre-Lab Discussion on DNA Fingerprints & ‘Forensic DNA Analysis’ Video @ http://www.teachersdomain.org/resource/tdc02.sci.life.gen.sheppard/ Answer the following questions: What does the DQA1 DNA test identify? What are the advantages and disadvantages of this method? Can the results of this test accurately pinpoint the source of the blood? Why or why not? 2. Go to the following site: http://www.pbs.org/wgbh/nova/sheppard/analyze.html Before doing the activity, read the following background information: Background Essay: Create a DNA Fingerprint In the last 15 years, DNA has played an increasingly important role in our legal system. Tissue evidence is now routinely collected during criminal investigations in hopes that it will provide genetic clues linking suspected criminals to crimes. DNA profiles help forensic investigators determine whether two tissue samples -- one from the crime scene and one from a suspect -- came from the same individual. Fortunately, the genetic comparison doesn't require that investigators look at all of the DNA found in the tissue samples. That would take months or even years. Instead, by marking a small number of segments of DNA in one sample and then checking for the presence or absence of those segments in the other sample, investigators can say with some assurance whether the samples are from the same person. How do they do it? Investigators use chemicals to cut the long strands of DNA into much smaller segments. Each segment has a specific length, but all of them share the same repeating sequence of bases (or nucleotides). The chemicals cut the segments at the beginning and at the end of the repeating string of nucleotides, so one segment might be ATCATCATCATCATC, for example, while another might be ATCATC. (The DNA segments used in forensic investigations are, of course, much longer than this.) Investigators use a process called gel electrophoresis to separate these repeating segments according to length. Next, they introduce a small set of radioactive "markers" to the sample. These markers are segments of DNA of known length, with bases that complement the code of, and bind to, sample segments of the same length. The sample segment above (ATCATCATCATCATC), for example, would be tagged by a marker with the complementary code TAGTAGTAGTAGTAG. Markers that do not bind to sample segments are then rinsed away, leaving in place only Spring 2011 those markers that bound to complementary sample segments. Photographic film, which darkens when exposed to the radioactive markers, identifies the location of all marked sample segments. This film, then, becomes the DNA "fingerprint" that forensic investigators analyze. The final step is a relatively simple matter of lining up the sample profiles side by side and comparing them for the presence or absence of segments with particular lengths. The more segments the two samples have in common, the more likely it is that the samples came from the same person. Answer the following questions: Describe the process of DNA fingerprinting? In what ways is it like actual fingerprint and in what ways is it different? How conclusive is the evidence of DNA fingerprinting? Where is there possibility for error? 3. Read the following article on ‘How DNA Evidence Works’ @ http://www.teachersdomain.org/assets/wgbh/tdc02/tdc02_doc_howdnaevid/tdc02_doc_howdnaev id.pdf Answer the following questions: DNA fingerprinting is only the first step in proving a suspect's DNA matches crime scene DNA. What is the second, and why is it important? What does non-coding DNA mean? Why is it important to create DNA profiles that include VNTRs from both maternal and paternal chromosomes in a chromosome pair? Why do you think DNA profiles produce discrete bands on a gel, instead of long solid streaks? [Hint: Think about what makes an individual band travel down the gel during electrophoresis.] Examine the DNA "ladders" on the gels. What do you think they are, and why do you think they are there? What can DNA profiles be used for, besides proving guilt or innocence in a courtroom? What to turn in when done with all 3 activities: You will turn in question/answer sets for all 3 activities listed above. Each student will turn in their OWN answers. Keep this sheet to study for questions for the test. You will work in groups of 2-3 and have 2 days to complete all 3 of these activities in class.