Lesson 10 of 15
Objective: SWBAT extract DNA from a variety of materials to explain how DNA is extracted to be used in forensic science.
I start each class period in this unit with a warm-up activity that targets forensic science concepts and other skills (observation, problem-solving, etc.) Not only does this get the students in the frame of mind necessary to address the field of forensics, but it also introduces key vocabulary they will use throughout the unit in a more relevant way. In addition, this activity allows students to refine their research skills as they perform quick internet searches to find the correct answers. By using the attached weekly Answer Sheet* and passing it out as they enter the classroom every Monday morning, not only can I save paper, but I can also provide a routine that allows students to begin without prompting, waiting for paper, or asking things such as, "What do we do?" and, "Where do we write our answers?"
For this particular lesson, I have decided to utilize a Video Challenge entitled, DNA Evidence (CODIS), in which students watch a short video clip about forensics and follow up by answering an assortment of trivia questions.
After providing about 2-3 minutes to choose the correct answers, we go over them together and discuss the information provided. I help students to define key terms and providing background knowledge necessary to help students understand the questions. However, I do not spend as extended period of time on this portion, as it is just meant to be an activator and not necessary to understanding the core of the lesson at this time.
*Challenges and answer sheet courtesy of http://sciencespot.net/Pages/classforscistarters.html
I start this portion of the lesson by having the students watch two short video clips. The first video, DNA Structure, explains the structure of DNA and the second video, How Does DNA Fingerprinting Work, explains how DNA can be used in crime scene investigations. This will provide foundational knowledge and catch the student’s interest by providing a connection between DNA structure and a real world application.
After watching the videos, I have students write down a least 2 questions they have about DNA and/or how it relates to forensics. I collect their questions and keep them in a safe place. While we do not read their questions now, I will refer back to them later in the lesson as a way for students to self-assess their learning.
Next, I explain that students will have the chance to perform a DNA extraction today. I ask volunteers to define the terms "extraction" or "extract". After getting the correct definition from a volunteer student, I ask all of the students to consider what DNA extraction might mean. After giving 1-2 minutes of think time, I explain tot he students that DNA extraction is the process of taking DNA out of a living thing, such as a plant or animal.I tell them that they will get two choose from three different processes to extract their DNA.
I direct the students to the videos, which I have placed on my website*. I have them form groups of 3-4, and have view all three videos. Once they have viewed each video, I have each group select which activity they would like to perform in order to extract their DNA.
Once each group has selected an activity, I pass out the DNA Extraction Lab. I explain that students must watch their chosen activity video again and use it to determine the materials and procedure they will need to follow. They will list each of these on the lab guide, and use it to perform the day's experiment. (For more information on this process, please see my reflection.)
Once the students have their lab guide completed and feel they are ready to perform their extraction, one student from the group gathers the materials and they get to work!
*The videos above are small, and not easily viewable for the students. I have provided the URL's to each video below so that you may embed or link them to a place that is easily accessible for your students.
This activity has been adapted from learn.genetics.utah.edu.
Each group will pair up with another group to compare their results and to read and discuss the "How does this Happen" portion of their lab. After completing in groups, we discuss as a class, comparing classwide results and discussing how each group differed in procedures, materials, observations, and results.
Next, I have the students who completed the human DNA extraction lab find another group to join, and teach the other groups how to perform this extraction. Because they are all pretty familiar with the overall process of DNA extraction, this should not take more than 5-10 minutes. As each group finishes, I pass out one small glass vial to each student, so that they may save their DNA to wear as a necklace and keep forever! (Just be sure to have the students fill their vials with isopropyl alcohol prior to closing.)
If time permits, I also show the video Employer Mandates DNA Testing, which explains how DNA tests were used for a very creative and unique way! BUT, remember before you use a video in your classroom watch it yourself. Some schools might object to aspects of this video.
Next, we revisit the questions that the students wrote at the beginning of the lesson. I read a few aloud at random, and ask students to Turn and Talk, forming a response. We share responses, based on the knowledge we have uncovered in the lab. While I facilitate discussion, I don't provide my own thoughts unless students get stuck on a topic or go off on a tangent.
In order to independently assess the learning that has taken place, students will respond in writing to a series of reflection questions, including the following:
- Explain why it is necessary to pulverize the fruit.
- Explain in your own words why a soap solution is used.
- Explain in your own words why rubbing alcohol is used.
- Explain in your own words why salt is used.
- Design a procedure to isolate DNA from a blood sample. Why would this procedure be useful?
These questions vary in the level of thinking, as they require students to explain, evaluate, and design, based on the content they have been investigating in this lab. Because of the diverse entry points of these questions, all students should have success in demonstrating their learning and understanding of the content.