Who Dunnit? The Case of the Missing Laptop

Overview & Concepts

The Case of the Missing Laptop is designed to be used as a unit.  It begins with a story about a petty high school crime and some DNA evidence found at the crime scene.  Students are taken through a problem-solving process as they learn techniques that would help them assess the DNA evidence from the crime scene to identify the perpetrator. The unit leads students through DNA extraction, PCR, Restriction Enzyme Digestion, Gel Electrophoresis, examination of LightCycler data, and DNA Fingerprinting.  Along the way are virtual labs as well as wet lab protocols.  The unit concludes with some reflection questions and ultimately invites ethical analysis of DNA sequencing application for the mass populus.

Grade Level: 

Concepts Covered: 

DNA extraction, polymerase chain reaction (PCR), PTC genetic testing, restriction endonucleases, gel electrophoresis, SNP data analysis from LightCycler Real-PCR, DNA fingerprinting

Prior Knowledge Required: 

DNA Structure, DNA replication, gene expression, genotype/phenotype, Mendelian genetics, dominant/recessive traits

Activity Notes

Days to Teach: 

Approximately 9-10 periods.


For DNA Extraction:

  • 10 mL saline solution (.9% NaCl)
  • 500 μl 10% Chelex solution
  • Sample cup
  • Marker
  •  2 1.5-mL microtube with locking lid
  •  Floating tube rack in boiling water
  • 2 clean micropipette tips
  • Centrifuge

For PCR Lab:

  • 2.5 μl of your DNA cheek cell sample from previous lab (store on ice)
  • PTC primer/loading dye mix (store on ice)
  • Ready-To-Go PCR beads in .2 mL tube
  • Marker
  • Micropipet (1-100 mL size) and tips
  • Microtube rack
  • Thermal cycler
  • Ice

Restriction Enzyme Digest Lab:

  • PCR product from previous lab (stored on ice)
  • Restriction enzyme HaeIll (stored on ice)
  • Marker
  • 1.5 mL micocentrifuge tubes
  • Micropipet and tips (1-20 µl)
  • Microtube rack
  • Thermal cycler
  • Ice

Gel Electrophoresis Lab:

  • Undigested PCR product from Part III, stored on ice
  • HaeIII digested PCR product from Part III, store on ice
  • pBR322/BstNI marker, stored on ice
  • 2% agarose in buffer
  • 500 mL buffer
  • Marker
  • 1.5 mL microcentrifuge tubes
  • Micropipet and tips (1-20 µl)
  • Microtube rack
  • Gel Electrophoresis chamber
  • Staining trays
  • Light transilluminator
  • Water bath (60°C)
  • Ice


Teaching Tips / Activity Overview: 

The document Missing Laptop Mystery Lesson Plan contains all the student worksheets needed for the unit.

  • Lesson 1: DNA Extraction
    • Pre-Lab: 15 minutes
    • DNA Extraction: 75 minutes
    • Homework 1: 25 minutes
  • Lesson 2: PCR
    • PCR Lab: 45 minutes to prepare amplicon, cycling will be complete by the next day
  • Lesson 3: Restriction Enzymes
    • Restriction Enzyme Digest Lab: Approx. 30 minutes- samples can cycle and be stored frozen for the next day's lesson
    • Homework: 20-25 mins
  • Lesson 4: Gel Electrophoresis
    • Gel Electrophoresis: If gels are made and poured ahead of time before class- then activity should take approximately 50 minutes.
    • If gels will be made by students, alot for 90 minutes.  Gel staining can also go on longer and UV illumination can take place the following day.    
    • Analysis Questions may be assigned as a homework as well.
  • Lesson 5 LightCycler Blood Typing: 25-30 minutes
  • Lesson 6 LightCycler Eye Color: 15-20 minutes
  • Lesson 7 DNA Fingerprinting: 25-30 minutes for virtual lab and Part II; 30-45 minutes to thoroughly answer Part III Reflection Questions


Homework 1 and 2 assess the knowledge of the central dogma of the PCR and Gel Electrophoresis protocols.  There is also a virtual DNA fingerprinting activity that serves as a formative assessment as well.  The reflection questions provide a good summative assessment as they cover both content and provide extrapolation and prompt further research.


  • Students can research the current topic of personal genome sequencing and engage in a debate about the pros and cons of having this information and technology available to the public.
  • Students can research and debate the ethics of patented genes and scientific progress.


  • Genetic Science Learning Center of University of Utah: http://learn.genetics.utah.edu/Provides a multitude of virtual labs, animations, background information, articles, and lesson plans concerning genetics and technology.
  • NOVA Education from PBS: http://www.pbs.org/wgbh/nova/teachers/Hosts a variety of student interactives, video clips, as well as lesson plans.


This activity was developed by K. Lindstrom. Some background material, LightCycler data, and all lab protocols derived from Franklin & Marshall Bioinformatics 2012 Seminar Handbook. Sources for other background material derived from Learn Genetics from University of Utah, NOVA from PBS.org. Storyline is original content.

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