DNA Forensics for Exoneration

In this lesson, students explore DNA fingerprinting through the true case of Darvin Castro Santos, who was wrongfully convicted of robbery in 2012 and was exonerated in 2021, in part by newly analyzed DNA evidence. After learning about the work of the National Registry of Exonerations and the specifics of Darvin’s case, students use restriction digest and gel electrophoresis to determine whether or not Darvin’s DNA was at the crime scene. The resources for our previous lesson, “”The Case of the Missing Klay Thompson Jersey”” are available under ‘Resources’.

The online version of this lesson follows the Klay Thompson scenario and includes point of view videos for the lab portion. Students use sample results to write a claim about whose DNA was at the scene of the crime and support it with evidence and reasoning.


Learning Objectives

  • Describe how DNA was used to exonerate Darvin Castro Santos, who was wrongfully convicted of robbery in 2009.
  • Explain how restriction enzymes and gel electrophoresis can be used to create unique DNA fingerprints between individuals

Prior Knowledge

  • Getting Started Series Parts 1-3 from BABEC to learn about DNA extraction, Micropipetting, and gel electrophoresis
  • Variation in DNA sequence (order of bases) exists among humans and other organisms



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Disciplinary Core Ideas:

LS3.A – Inheritance of Traits
“…not all DNA codes for a protein…” The regions the restriction enzymes cut vary among individuals and typically do not code for a protein

LS3.B – Inheritance of Traits
“…distribution of traits on genetic and environmental factors”

Science and Engineering Practices:

  • Planning and Carrying out Investigations
  • Analyzing and Intercepting Data Patterns

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Paradise Valley HS
Phoenix, AZ

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Burton HS
San Francisco, CA

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Gianne Souza
Lincoln HS
San Francisco, CA

The online resources are SO well done! The best I have ever had. Very little modification to make them clear and easy to follow. I have done two BABEC lessons and they are so well made that they made teaching online fun again.

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Burlingame HS
Burlingame, CA

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Marianne Gudmundsson
Glenbrook South HS
Glenview, IL

Well organized and scaffolded; flexible structure and can be used partially or as a whole. This unit can be used as is...superbly written and thought out...incorporates many skills and allows student collaboration and student choice/voice.

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South San Francisco HS
South San Francisco, CA

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Capuchino HS
San Bruno, CA

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