In the forensics module, students learn how DNA is analyzed by forensic scientists in order to link a DNA sample to a particular individual. To do this, forensic scientists use powerful molecular biology techniques such as PCR, restriction digests and gel electrophoresis. To learn more about DNA and how it is used by forensic scientists, students will isolate their own DNA from saliva!  Using their new-found understanding of DNA and forensics techniques, students will help solve the case of the missing mascot.  Whodunit?

Teacher's Guide

Case of the Missing Mascot

This module begins with students reading a short skit informing them that Rival High School has kidnapped their mascot before the big Homecoming football game!  The Rival senior class left a ransom note which contained a stray strand of hair from the perpetrator.  To solve the crime, students must learn more about DNA and forensic science!

DNA Review

The first step to solving the crime is to learn some basics about DNA:  it’s structure, composition, and chemical properties. There are over 3 billion nucleotide bases in the human genome, however each person’s DNA is 99.9% identical to anyone else on earth.  It is this 0.1% difference that is the focus of Forensic Scientists who use the uniqueness of an individual’s DNA to generate a unique DNA “fingerprint” which can link a person to a crime scene.

DNA Isolation from Saliva

DNA can come from a variety of sources, and in this module students extract their own DNA from saliva using common household items – soap, salt, and rubbing alcohol. The extraction steps reinforce important concepts about DNA’s location (in cells) and chemical properties (negatively charged, hydrophilic).  At the end of this exercise students will see their own DNA up close and personal!

Analysis of DNA by Forensic Scientists

After isolating DNA, this module then introduces students to important molecular biology techniques used by Forensic Scientists to analyze DNA samples.  These include Polymerase Chain Reaction (PCR) which enables scientists to “amplify” DNA and get lots of information from a tiny amount of DNA from a crime scene.  Scientists then use special proteins called “restriction enzymes” which cut DNA into fragments of unique sizes that vary from individual to individual. The last step of the analysis involves separating the DNA fragments of differing sizes using gel electrophoresis.

Solve the Crime!

Equipped with an understanding of common Forensic Science methodologies, students use these skills to solve the case of the missing mascot!  Whodunit?

The Innocence Project

Crime shows like CSI have made the idea of using DNA evidence to solve crimes very popular.  However, advances in Forensic Science have also resulted in many innocent people being released from prison after being wrongly convicted.  The Innocence Project is an organization devoted to re-opening cases that would benefit from the addition of DNA evidence.  One specific example is highlighted in the popular book, Picking Cotton.  This book documents the events that led to an innocent North Carolina man, Ronald Cotton, being released from jail years after being wrongly accused of assaulting Jennifer Thompson.  Ronald and Jennifer now tour the country together lobbying for eyewitness testimony reform and for increased use of DNA evidence.