Exam (elaborations) GIZMO DNA Profiling.pdf Gizmo Student Exploration

Vocabulary : DNA polymerase, DNA profiling, gel electrophoresis, gene, mutation, non-coding region, polymerase chain reaction, primer, short tandem repeat Prior Knowledge Questions (Do these BEFORE using the Gizmo.) In 1985, Darryl Hunt was convicted of murder. While Hunt was in jail, a new method for analyzing DNA evidence was invented. The DNA evidence on the victim did not match Hunt’s DNA but did match that of another prisoner. After 19 years spent behind bars, Hunt was finally declared innocent and released from prison in 2004. 1. DNA is used to tell people apart. What aspects of DNA do you think make this possible? - The lengths of the repeated sequences in DNA - The DNA sequences themselves 2. What are some possible uses for technology that can identify people based on their DNA? - Gel electrophoresis Gizmo Warm-up DNA profiling does not just compare people’s entire genome side by side. Instead, a very particular part of the DNA is compared. In the DNA Profiling Gizmo you will learn about the differences in DNA that make DNA profiling possible and you will use that knowledge to design your own DNA profiling test. Click on the crime lab in the Forensic training section. You are looking at a strand of DNA. DNA contains genes and non-coding regions between genes. Click on Non-coding A. 1. You are looking at a portion of the non-coding A section for three different people. Are these sections the same or different? Explain. - The sections are different. Person 1 has the longest section, person 3 has the second-longest section and person 2 has the shortest section. a. Click Previous then click on Gene A. Are there differences in gene A for the three people? GIZMO DNA P Gizmo Student Exploration - Person 1 and Person 3 have identical sequences in their gene A. On the other hand, the sequence of nucleotides in person 2 differs from both persons 1 and 3. In one section, persons 1 and 3 have the base pair of C and G whereas person 2 has the base pair of A and T. Activity A: Forensic training Get the Gizmo ready : ● Click on Forensic training and Start again . Introduction: In this activity, you will learn about the principles and techniques that make DNA profiling possible. Genes code for specific traits. In people, the DNA sequences for most genes are nearly identical, since any change could result in a harmful disorder. The areas between genes do not code for any essential traits, so a change to the DNA sequence doesn’t have any major consequences. As a result, these regions tend to be very different for different people. Question: How can the differences in DNA be exploited to perform DNA profiling? 1. Observe : Click on non-coding A. What do you see in the middle of each of the three DNA sequences? - I see repeated sequences (TAAA and ATTT) in all three DNA sequences. 2. Compare : Turn on Show short tandem repeats (STRs) . An STR is a short, repeated sequence of DNA, like TAAA. They can be repeated any number of times without affecting the traits of the person. Different people usually have different numbers of repeats. What does this do to the length of each person’s non-coding regions? - The more STRs a person has in their DNA, the longer their non-coding regions. Vice versa, the fewer STRs a person has, the shorter their non-coding regions. 3. Create : Your goal is to make copies of the STR region. To do this, you will make primers that surround the STR region. A primer is a short sequence of DNA that acts as a starting point for DNA replication. Click Next . Click on person 1’s DNA to separate the two strands. Drag along the AAGGC nucleotides, and then the TCGCC nucleotides to create primers. Click Next . The Gizmo will add the same primers to the two other people. What do you notice about where the primers attach in each person? - In all 3 people, the primers attach to the same parts of the DNA strand. One primer attaches to the beginning of the top strand and the other primer attaches to the end of the bottom strand for all 3 individuals. 4. Observe Click Next. An enzyme called DNA polymerase uses the primers as a starting point to copy the DNA. Copying DNA using primers is a technique called Polymerase chain reaction (PCR) . Click Next again. The DNA segments are copied millions of times. What do you notice about the lengths of the copied DNA strands? - I notice that the lengths of the copied DNA strands are different for each person. Activity A (continued from previous page) 5. Compare : Click Next . Gel electrophoresis is used to separate DNA strands of different lengths. An electric current is passed through the gel. As the current moves from top to bottom, it pulls the DNA and loading dye along with it. Click on the power box to turn it on. A. Which person’s DNA band travelled the farthest? Shortest? - Person 2’s DNA band travelled the farthest, person 3’s DNA band travelled the second farthest and person 1’s DNA band travelled the shortest. B. Turn on Show labels. What do you notice about the length of the DNA versus the distance it travelled down the gel? - The longer the strand of DNA, the shorter distance the strand travelled. Vice versa, the shorter the strand of DNA, the longer distance the strand travelled. C. Can you identify people by comparing the length of STR regions on a gel? Explain. (2) - Yes, you can identify people because the length of STR regions on DNA varies from person to person. However, it is possible for two or more people to have the exact same length of STR regions. This is why the identification process also depends on the circumstances of the case and the evidence found. 6. Observe : Click Next . Then select Gene A . A. Does gene A have any STRs? - No, gene A does not have any STRs. Because genes are segments of DNA that hold the instructions for producing proteins, they usually don’t have large variable regions like STRs. B. Are there any differences in gene A between the individuals? Look carefully - Person 1 and Person 3 have identical sequences in their gene A. On the other hand, the sequence of nucleotides in Person 2 differs from both persons 1 and 3. In one section, persons 1 and 3 have the base pair of C and G whereas person 2 has the base pair of A and T. Genes may contain small mutations that don’t affect the length of the segment. C. Create primers and copy the DNA. What do you notice about the length of the duplicated regions? - The length of the duplicated regions is the exact same for all three individuals. D. Click Next and turn on the gel electrophoresis apparatus. What do you notice about the position of the band? - The position of the band is the same for the three people. It is positioned a little bit below 30 base pairs. E. Can you identify people by comparing the length of genes on a gel? Explain. (2) - No, you cannot identify people by comparing the length of genes on a gel. This is because, unlike STRs, gene lengths do not vary between individuals. Most genes are the same in all people. 7. Summarize : How can PCR and gel electrophoresis be used to identify people? - PCR is used to make millions of copies of an individual’s DNA. This is important because sometimes there may be a low concentration of DNA. After the copies are made, the DNA can be analyzed using gel electrophoresis. The gel separates the DNA of different people based on size or length. Each individual’s DNA varies by size, making PCR and gel electrophoresis effective methods of identifying people. Activity B: Design and test primers Get the Gizmo ready : ● Select Design primers on the left. Introduction: To identify people based on DNA, copies of certain segments of DNA are compared using gel electrophoresis. In this activity, you will design primers that will copy segments of DNA that will help to identify people. Question: How can you use your knowledge to create a DNA profiling test? 1. Predict : Gel electrophoresis distinguishes DNA segments by length. To identify people by DNA, is it better to make copies of genes or non-coding segments? Explain. - To identify people by DNA, it is better to make copies of non-coding segments rather than genes because, for most individuals, genes are the same exact length. On the other hand, the length of STRs on the non-coding segments varies between individuals making it a better option. 2. Create : Pick a section of DNA you want to copy and follow the directions to create primers. A. Click Preview primer. Did the DNA copy properly? - Yes,