Most of the DNA in the human genome does not encode proteins or RNA. Some of this

Transcription

1 DNA FAMILY RELATIONSHIP ANALYSIS (GENETICS) Most of the DNA in the human genome does not encode proteins or RNA. Some of this DNA consists of regulatory sequences, which help control the processes of transcription and translation, but most of it actually consists of sequences whose functions are not yet fully understood by scientists. This DNA includes introns, stretches of noncoding DNA that are often found within the coding sequences of genes. Some of this noncoding DNA also consists of repetitive DNA, which is a nucleotide sequence (e.g., ATTGGCC) that repeats several times (e.g., ATTGGCC-ATTGGCC-ATTGGCC). These repetitive sequences are called short tandem repeats (STRs). The exact number of times a specific sequence repeats at a specific site in genome differs from individual to individual. The size of an STR (e.g., the number of times a sequence repeats) at a specific site can therefore be used as a genetic marker. These genetic markers can then be used to determine if two people are related or not. There are several different genetic markers that scientists use to help determine family relationships (e.g., D21S11 and D7S820). Everyone inherits two copies of these various genetic markers: one copy from the father and one from the mother. The two copies of each marker are usually different. Therefore, scientists can often determine which version of a particular marker was inherited from a particular parent. This information can be used to determine if two people are related or not. Mr. and Mrs. H. had five children: three sons and two daughters. Tragically, the H. s youngest son was abducted from them 20 years ago. This child was only six years old at the time and the police never found him or the person who took him. Recently, a young man named Jeff M., who is in his mid-20s, has contacted the H. family. He claims that he is the boy who was abducted from them. However, the H. family is skeptical and has requested a genetic test to determine if Jeff M. is related to them or not. Unfortunately, Mr. H. died in car accident several years ago. A DNA sample, as a result, can only be collected from Jeff M., Mrs. H., and the family s four children. Your task is to use the results of an STR family relationship test that was conducted using DNA samples from these six individuals to determine if Jeff M. is the biological offspring of Mr. and Mrs. H. So the guiding question of this investigation: Is the H. family related to Jeff M.? With your group, develop a claim that best answers this question. Once your group has developed your claim, prepare a whiteboard that you can use to share and justify your ideas. Your whiteboard should include all the information shown in the Figure.1 (p. 6). To share your work with others, we will be using a round-robin format. This means that one member of the group will stay at your workstation to share your group s ideas while the other group SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES

2 DNA SECTION 1: GENERATE AN ARGUMENT FAMILY RELATIONSHIP ANALYSIS members go to the other groups one at a time in order to listen to and critique the arguments developed by your classmates. Remember, as you critique the work of others, you need to decide if their conclusions are valid or acceptable based on the quality of their claim and how well they are able to support their ideas. In other words, you need to determine if their argument is convincing or not. One way to determine if their argument is convincing is to ask them some of the following questions: How did you analyze or interpret your data? Why did you decide to do it that way? Figure.1. Components of the Whiteboard The Research Question: Your Claim: Your Evidence: Your Justification of the Evidence: How do you know that your analysis of the data is free from errors? Why does your evidence support your claim? Why did you decide to use that evidence? Why is your evidence important? How does your justification of the evidence fit with accepted scientific ideas? What are some of the other claims your group discussed before agreeing on your claim, and why did you reject them? 6 NATIONAL SCIENCE TEACHERS ASSOCIATION

3 DNA FAMILY RELATIONSHIP ANALYSIS Results From STR Family Relationship Analysis Test Figures.2. represent the results from an STR family relationship test. The profile at each DNA marker or STR region (e.g., D13S317, THO1) appears as one or two bars. The height of each bar represents the number of times that the STR is repeated in that person. For example, in Mrs. H., the STR at the D13S317 locus is repeated 10 times on one chromosome and 14 times on the other. The STR profile for Mrs. H. at the D site is therefore listed as 10, 14. Figure.2. DNA Marker: D13S317 (Found on Chromosome 13) Mrs. H Child 1 Child 2 Child 3 Child 4 Jeff M. Figure.3. DNA Marker: TH01 (Found on Chromosome 11) Mrs. H. Child 1 Child 2 Child 3 Child 4 Jeff M. SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES 7

4 DNA SECTION 1: GENERATE AN ARGUMENT FAMILY RELATIONSHIP ANALYSIS Figure.4. DNA Marker: D21S11 (Found on Chromosome 21) Mrs. H. Child 1 Child 2 Child 3 Child 4 Jeff M. Figure.. DNA Marker: D7S820 (Found on Chromosome 7) Mrs. H. Child 1 Child 2 Child 3 Child 4 Jeff M. 8 NATIONAL SCIENCE TEACHERS ASSOCIATION

5 DNA FAMILY RELATIONSHIP ANALYSIS A lab technician used the protocol in Figure.6 to create each gel. Figure.6. Protocol Used to Create Each Gel Samples of DNA from the adults and children Mrs. H Child 1 Child 2 Child 3 Child 4 Jeff M. A restriction enzyme is added in order to cut the DNA into fragments Mrs. H Child 1 Child 2 Child 3 Child 4 Jeff M. Each sample is loaded into to a different well on a gel Mrs. H Child 1 Child 2 Child 3 Child 4 Jeff M. Electrophorese DNA samples at 100 Volts for 30 minutes. Then add a stain to the gels to make the bands visible. SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES 9

6 DNA FAMILY RELATIONSHIP ANALYSIS: What Is Your Argument? In the space below, write an argument in order to persuade another biologist that your claim is valid and acceptable. As you write your argument, remember to do the following: State the claim you are trying to support Include genuine evidence (data + analysis + interpretation) Provide a justification of your evidence that explains why the evidence is relevant and why it provides adequate support for the claim Organize your argument in a way that enhances readability Use a broad range of words including vocabulary that we have learned Correct grammar, punctuation, and spelling errors 60 NATIONAL SCIENCE TEACHERS ASSOCIATION

7 DNA FAMILY RELATIONSHIP ANALYSIS TEACHER NOTES Purpose The purpose of this activity is to help students understand the molecular basis of heredity and the role that DNA technology can play in solving social problems. This activity also helps students learn how to engage in practices such as constructing explanations, engaging in argument from evidence, and communicating information. This activity is also designed to give students an opportunity to learn how to write in science and develop their speaking and listening skills, which are important goals for literacy in science (see Standards Addressed in This Activity for a complete list of the practices, crosscutting concepts, core ideas, and literacy skills that are aligned with this activity). The Content and Related Concepts Most of the DNA in eukaryotic genomes does not encode proteins or RNA (Campbell and Reece 2002). Although some of this DNA consists of regulatory sequences, which help control the processes of transcription and translation, most of it actually consists of sequences whose functions are not yet understood. This DNA includes introns, stretches of noncoding DNA that are often found within the coding Figure.7. Coding and Noncoding Sequences of DNA DNA Sequence Gene pre-mrna mrna Gene 1 Non-coding sequence (location of repetitive DNA) Gene 2 Promotor Exon Intron Exon Intron Exon Intron Exon Transcription Intron Exon Intron Exon RNA Processing Cap and tail added; introns removed and exons are spliced together sequences of genes (see Figure.7). Even more of the noncoding DNA consists of repetitive DNA, which is a nucleotide sequence that is present in many copies in the genome and usually not found within a gene. There are two types of repetitive DNA. The first type of repetitive DNA is called short tandem repeats (STRs). STRs consist of a 1 10 base pair sequence (e.g., GTTAC) that repeats (e.g., GTTAC-GTTAC- GTTAC) as many 100,000 times at a specific location. The second type is called interspersed repetitive DNA. The repeated units of this type of DNA are not next to each other; instead they are scattered throughout the genome. A single unit of interspersed repetitive DNA is usually 100 1,000 base pairs long, and the dispersed copies are usually very similar but not identical to one another. SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES 61

8 DNA SECTION 1: GENERATE AN ARGUMENT FAMILY RELATIONSHIP ANALYSIS TEACHER NOTES The DNA sequence of every person, except for identical twins, is unique, but the number of STRs at a specific location is passed down from parents to offspring. As a result, the number of STRs at different locations in the genome can be used as a genetic marker for a DNA fingerprint. An individual s DNA contains two copies of each of these markers: one copy is inherited from the father, and one is inherited from the mother. As a result, the two versions of a marker that an individual has at a specific location can differ in length, depending on which version of the marker he or she inherited from his or her parents. These differences allow scientists to determine if two or more people are related or not. It is important to note, however, that scientists must examine several different markers before they can draw any conclusions about familiar relationships because two people can share the same marker even when they are not related. Scientists therefore typically use 16 or more markers in order to create a DNA fingerprint and to conduct a family relationship analysis, because the likelihood of two unrelated individuals sharing several different markers is quite small. In this activity, the students are asked to determine if Jeff M. is the child of Mr. and Mrs. H. based on the results of STR analysis from four different markers: TH01, D21S11, D7S820, and D13S317. The results of the analysis are provided in Table.1. In this table, the version of the STR that could have been inherited from Mrs. H. is in bold while the version of the STR that could have been inherited from Mr. H. is in italics. For the D13S317 marker, Jeff M. has an STR in common with Mrs. H. (3) and an STR in common with Child 2 and Child 3 (21), which could have been inherited from Mr. H. For the TH01 marker, Jeff M. has an STR in common with Mrs. H. (21) and an STR in common with Child 2 and Child 4 (12) that could have been inherited from Mr. H.. For the D21S11 marker, Jeff M. does not have an STR in common with Mrs. H. but has an STR in common with Child 2, Child 3, and Child 4 (21) that could have been inherited from Mr. H. Finally, for the D21S11 marker, Jeff M. has an STR in common with Mrs. H. (17) and has an STR in common with Child 1, Child 3, and Child 4 (9) that could have been inherited from Mr. H. Jeff M., therefore, is not the biological child of Table.1. Results of STR Analysis Marker Mrs. H. Child 1 Child 2 Child 3 Child 4 Jeff M. D13S317 14, 3 14, 3 21, 3 14, 21 14, 3 3, 21 TH01 21, 6 6, 6 21, 12 6, 21 6, 12 12, 21 D21S11 16, 16, 10 16, 21, 21 16, 21 9, 21 D7S820 22, 17 22, 9 22, 22 17, 9 22, 9 17, 9 62 NATIONAL SCIENCE TEACHERS ASSOCIATION

9 DNA FAMILY RELATIONSHIP ANALYSIS TEACHER NOTES Mr. and Mrs. H., although he has several STRs in common with Mrs. H. and her children at all four genetic markers. However, a case could be made that the unique STR that Jeff M. has at marker D21S11 (9) is a mutation of the STR (10) that Child 1 inherited from Mr. H., or the STR that Child 1 has (10) is a mutation of the STR (9) inherited by Jeff M. Curriculum and Instructional Considerations This activity is best used as part of a unit on genetics. However, it should only be used to give students a chance to apply their understanding of Mendelian inheritance and DNA structure in an unfamiliar context. It is therefore important for the teacher to introduce students to the concept of genes and the law of segregation as well as several different modes of inheritance such as co-dominance, incomplete dominance, multiple allele, polygenic, and sexlinked. Students should also understand the structure of DNA. Students will need a basic understanding of these ideas in order to be able to analyze and interpret the data that will be supplied to them during the activity. The focus of the explicit discussion at the end of the activity should focus on an aspect of the nature of science or the nature of scientific inquiry. For example, a teacher could discuss how a scientific explanation must be consistent with observational evidence about nature or how scientists rely on a wide range of methods (and not just experiments) to answer research questions using what the students did as an illustrative example. Recommendations for Implementing the Activity This activity takes approximately 100 minutes of instructional time to complete, but the amount of time devoted to each activity varies depending on how a teacher decides to spend time in class. For more information about how to implement the activity, see Appendix E on page 369. Table.2 (p. 64) provides information about the type and amount of materials needed to implement this activity in a classroom with 28 students with groups of four and groups of three. Assessment The rubric provided in Appendix B (p. 366) can be used to assess the arguments crafted by each student at the end of the activity. To illustrate how the rubric can be used to score an argument, consider the following example. This sample argument, which was written by a 10th-grade student, provides an accurate claim but the evidence and rational are rather weak. Jeff M. is the child of Mr. and Mrs. H.. I know this is right because the results of the DNA analysis proves it. Jeff M. had markers in common with Mrs. H. and all of Mrs. H. s children. Mrs. H. therefore has found her long lost son. DNA does nt lie. The content of the example argument is weak for several reasons. The student s claim (underlined) is sufficient (1/1) but inaccurate (0/1). The student, in addition, does not use genuine evidence (in bold) to support the claim (0/3). Instead, the student relies on an unsub- SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES 63

10 DNA SECTION 1: GENERATE AN ARGUMENT FAMILY RELATIONSHIP ANALYSIS TEACHER NOTES Table.2. Materials Needed to Implement the Activity in a Classroom of 28 Students Amount Needed With Material Groups of 3 Groups of 4 Whiteboards (or chart paper) Whiteboard markers (or permanent if using chart paper) Copy of Student Pages (pp. 9) * Copy of Student Page (p. 60) * 10 7 Copy of Appendix B (p. 366) * Teachers can also have students prepare their arguments in a digital medium (such as PowerPoint or Keynote). * Teachers can also project these materials onto a screen in order to cut down on paper use. stantiated inference as evidence. The student also does not include a sufficient justification of the evidence in his argument because he does not explain why the evidence is important by linking it to a specific principle, concept, or underlying assumption (0/2). Instead, he simply insists that his claim is accurate. The author uses scientific terms correctly (1/1) but includes phrases (e.g., I know this is right, the DNA analysis proves it ) that misrepresent the nature of science (0/1). The writing mechanics of the sample argument also need improvement. The organization of the argument is acceptable, because the arrangement of the sentences does not distract from the development of the main idea (1/1), although the argument is rather short. There are also some grammatical (0/1) and punctuation errors (0/1) in the argument. The overall score for the sample argument, therefore, is 3 out the 12 points possible. Standards Addressed in This Activity This activity can be used to address the following dimensions outlined in A Framework for K 12 Science Education (NRC 2012): Scientific Practices Developing and using models Constructing explanations Engaging in argument from evidence Obtaining, evaluating, and communicating information Crosscutting Concepts Patterns Cause and effect: Mechanism and explanation 64 NATIONAL SCIENCE TEACHERS ASSOCIATION

11 DNA FAMILY RELATIONSHIP ANALYSIS TEACHER NOTES Life Sciences Core Ideas From molecules to organisms: Structures and processes Heredity: Inheritance and variation of traits This activity can be used to address the following standards for literacy in science from the Common Core State Standards for English Language Arts and Literacy (NGA and CCSSO 2010): Writing Text types and purposes Production and distribution of writing Research to build and present knowledge Range of writing Speaking and Listening Comprehension and collaboration Presentation of knowledge and ideas References Campbell, N., and J. Reece Biology. 6th ed. San Francisco, CA: Benjamin Cummings. National Governors Association Center (NGA) for Best Practices, and Council of Chief State School Officers (CCSSO) Common core state standards for English language arts and literacy. Washington, DC: National Governors Association for Best Practices, Council of Chief State School. National Research Council (NRC) A framework for K 12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: National Academies Press. SCIENTIFIC ARGUMENTATION IN BIOLOGY: 30 CLASSROOM ACTIVITIES 6