Creating DNA's Fingerprint
Lesson 6 of 6
Objective: SWBAT apply their prior knowledge of the structure and function of DNA to investigate the process of DNA fingerprinting as it relates to our Biology curriculum.
Students will have the opportunity to build their prior understanding of DNA to a new level as they explore real-world applications using DNA fingerprinting. Students will explore the steps of gel electrophoresis in an online simulation and then use their new found knowledge to write a reaction to the statement: "When used correctly, DNA profiling is a powerful forensic tool." Students will obtain, evaluate, and communicate their findings about DNA and DNA fingerprinting.
Have a fun with this lesson as DNA comes to life and engages your students in real-world applications.
Students will watch this introductory video to activate prior knowledge of DNA structure of function to understanding the process of DNA fingerprinting.
Students will record at least ten interesting facts from the video clip.
At the conclusion of the video, students will have the opportunity to come to the front of the board to write their "most" interesting fact for the class to view. The only guideline for participation is that students cannot add a fact that has already been included on our class list of facts.
Students are encouraged to add at least five additional facts, so that their video notes will consist of at least 15 facts about DNA fingerprinting.
Students will get out a sheet of paper to record the DNA Fingerprinting Lecture Notes to become more informed on the process of DNA fingerprinting.
Extra Resources: This lecture topic always brings about a plethora of "what-if" questions from the students. It is a great idea to review the most obscure topics related to DNA fingerprinting in preparation of this lesson. Wikipedia has an informative page on this subject, as does the University of Arizona's Biology Project. In addition, California State University at Northridge has published an effective DNA fingerprinting presentation that offers a more in-depth introduction of the scientific process that is geared toward more advanced students/classes.
Helpful Hints: Don't be afraid of these engaging classroom discussions. The more questions students raise, the more engaged they are in your powerful lesson! Have fun with topic and if necessary work to investigate DNA fingerprinting and its application together.
Students will go to the University of Utah's Genetic Learning Center to complete the online Gel Electrophoresis Lab Activity. This online activity simulation will allow students to actively participate in the process of gel electrophoresis, as well as reflect on their experience by using the Gel Electrophoresis Simulation Handout.
Sample of Student Work
Background Information from The PBS NOVA Website:
Practical Application of DNA Fingerprinting (Southern Blot) - During 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.
The Process of DNA Fingerprinting - 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 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.
Making A Conclusion - 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.
At the conclusion of the online simulation, students will click on the link "Can DNA Demand a Verdict?" Student-pairs will read the three sections and take notes on significant details from the readings:
How can DNA be used to identify an individual?
Forensic DNA Analysis
Is DNA evidence alone enough to acquit or convict?
Homework: Students will write an informed response to the statement, "When used correctly, DNA profiling is a powerful forensic tool." Students will be asked to use specific details from today's lecture notes and Utah Genetics' online activity to demonstrate their support of the statement or provide evidence to refute the statement. The student responses should be a page in length and will be shared in class in class discussion/debate.
Sample of Student Work - Gel Electrophoresis - Students found this activity both informative and entertaining due to its realistic graphics and abundance of information. This online simulation is a great substitute for the "real" thing if your site does not have access to the technology to complete the gel electrophoresis activity. This activity can also be completed in class with collaborative partners or as a demonstration on the front projection screen led by the teacher. There are many strategies to include this resource into your curriculum for next year!
Differentiating DNA Fingerprinting Online Activities: Students who need to move at a slower pace with fewer details can use the PBS NOVA website to complete the Create a DNA Fingerprint activity using the Create a DNA Fingerprint Online Activity Participant Handout to guide their interactive experience.
Teacher Note: Due to the simplicity and introductory nature of the PBS NOVA activity, most students will accurately claim that Honey committed the crime that was investigated in the online simulation. This is a great opportunity to differentiate your instruction by allowing students separate activities that meet their learning needs.