DNA Profiling in Forensics

Curriculum Area: Science – Forensic Sciences (Grades 11-12)

Standards Alignment:

• NGSS HS-LS3-1: Ask questions to clarify relationships about the role of DNA and chromosomes in coding instructions for characteristic traits.
• NGSS HS-LS1-1: Construct an explanation based on evidence for how DNA structure leads to function in forensic applications.
• CCSS.ELA-LITERACY.RST.11-12.3: Follow precisely a complex multistep procedure when carrying out experiments.

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Lesson Breakdown

Duration: 5 Days (45-Minute Sessions)
Class Size: 24 Students

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Day 1: Introduction to DNA Profiling

Objectives

• Define DNA profiling and its forensic applications.
• Understand how short tandem repeats (STRs) are used in profiling.
• Discuss key court cases where DNA evidence was critical.

Lesson Plan

1. Engage (10 min):

   • Start with a case study: The role of DNA in The Innocence Project.
   • Class discussion: Can DNA evidence be wrong?

2. Explain (15 min):

   • Lecture with visuals on STR Analysis, Polymerase Chain Reaction (PCR), and gel electrophoresis.
   • Show a short clip explaining how DNA is collected at crime scenes.

3. Explore (15 min):

   • Students work in small groups analyzing anonymized DNA printouts of mock suspects.
   • They will determine which STR alleles match the evidence.

4. Exit Ticket (5 min):

   • One-minute journal: "What surprised you about DNA profiling today?"

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Day 2: DNA Extraction Lab Activity

Objectives

• Conduct a hands-on DNA extraction experiment.
• Identify the physical appearance of DNA.

Lesson Plan

1. Engage (5 min):

   • Ask: "If you could extract DNA from any object, what would you investigate?"

2. Explain (10 min):

   • Overview of DNA extraction process (lysis, precipitation, filtration).

3. Lab Activity (25 min):

   • Materials: Strawberries, dish soap, salt, rubbing alcohol, coffee filters.
   • Procedure:
     1. Mash strawberries to break cells.
     2. Use dish soap and salt mixture to break down membranes.
     3. Filter out larger particles.
     4. Add chilled alcohol to make DNA strands visible.

4. Wrap-Up (5 min):

   • Compare DNA samples.
   • Discuss where errors could occur in forensic labs.

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Day 3: Analyzing DNA Evidence

Objectives

• Interpret realistic STR electrophoresis results.
• Simulate the forensic investigation process.

Lesson Plan

1. Engage (5 min):

   • Show a gel electrophoresis result with unclear bands.
   • "Do two people ever have the exact same DNA profile?"

2. Explain (10 min):

   • Demonstrate the STR matching process between evidence and suspect profiles.

3. Activity: Analyst for a Day (25 min)

   • Students receive crime scene DNA bands on printed electrophoresis sheets.
   • Compare with four suspect profiles to determine guilt/innocence.
   • Justify findings in a mini courtroom debate.

4. Exit Slip (5 min):

   • "What would you change about how forensic labs process DNA?"

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Day 4: Introduction to Karyotyping

Objectives

• Define karyotyping and its forensic significance.
• Identify numerical and structural chromosomal abnormalities.

Lesson Plan

1. Engage (5 min):

   • "What if DNA doesn't provide a perfect match? What else can you analyze?"
   • Quick poll: Who knows their own karyotype?

2. Explain (15 min):

   • Describe how karyotyping is used in forensic investigations (e.g., identifying unknown remains, detecting genetic disorders).
   • Show real examples of chromosome maps from forensic casework.

3. Activity (20 min):

   • Students will simulate a forensic karyotyping analysis with scrambled chromosome sets.
   • They will match karyotypes to case profiles (e.g., an unknown victim of a crime).

4. Exit Ticket (5 min):

   • Reflect: How might karyotyping be useful in identifying unknown remains?

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Day 5: Karyotyping Challenge & Real-World Applications

Objectives

• Apply karyotyping skills to a forensic case study.
• Explain how chromosomes play a role in criminal and forensic investigations.

Lesson Plan

1. Engage (5 min):

   • Pose the question: "Could someone have an extra chromosome and not know it?"

2. Forensic Case Simulation (35 min):

   • Scenario: Investigators recovered remains from an unidentified crime scene.
   • Students receive three different sets of karyotypes.
   • Their task: Identify gender, possible conditions (e.g., trisomy 21), and possible leads in solving the case.
   • Group discussion: How might findings help law enforcement?

3. Reflect & Wrap-Up (5 min):

   • Discuss how DNA profiling and karyotyping work together in forensic science.
   • Final question: "What ethical problems could arise from karyotyping someone without consent?"

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Assessment & Extension

• Formative Assessments: Group discussions, exit tickets, and lab reports.
• Summative Assessment: A case study where students must solve a forensic mystery using DNA evidence.

Extension Activity (For Advanced Learners):

• Research an unsolved case where DNA evidence played a role.
• Identify what forensic challenges were present in profiling.
• Present findings in a mini mock trial presentation.

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Materials Needed

• Day 2: Strawberries, dish soap, salt, rubbing alcohol, coffee filters.
• Day 3 & 4: Printed STR electrophoresis gels, forensic DNA profiles.
• Day 5: Sample chromosomes for karyotyping activity.

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Final Thoughts

This immersive lesson plan allows students to step into the shoes of forensic investigators—from extracting DNA to identifying chromosomal patterns. By incorporating hands-on labs, debates, and case simulations, students will develop both critical thinking and analytical reasoning skills essential for forensic science. 💡🔬