FORENSIC DNA

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This session provides participants with a basic understanding of genetics and how forensic DNA is used in criminal investigations.

Category

  • Exploring: Law Enforcement
  • S. Department of Education: Law, Public Safety, Corrections & Security
  • U.S. Department of Education: Government & Public Administration

Objectives

By the end of this session, participants will be able to:

  • Describe the molecular basis of inheritance.
  • Identify where DNA is located within the cell.
  • Discuss the helical nature of DNA.
  • List the four nitrogenous bases that make up DNA and describe the concept of base pairing.
  • Distinguish between a gene and a chromosome.
  • Demonstrate how DNA evidence is collected and how DNA standards are taken from suspects.
  • Perform DNA extraction from cheek cells.
  • Identify the percentage of DNA that is useful for forensic science purposes.
  • Discuss how the sample size requirements have changed since the invention of forensic DNA analysis.
  • Describe how restriction enzymes act like molecular scissors.
  • Explain what electrophoresis is and how it’s used to separate DNA fragments.
  • Interpret the results of gel electrophoresis.
  • Compare and contrast CODIS and NDIS.

Supplies

  • (1) computer with internet access
  • For each participant:
  • (1) pair of nitrile or latex gloves (check for allergies before using latex gloves)
  • (1) bottle of stage blood or reddish-brown liquid with the consistency of blood
  • (1) object that the stage blood can be spread on (countertop, pencil, etc.)
  • (2) cotton swabs
  • (1) eye dropper bottle containing water
  • (1) bottle of drinking water (500 ml)
  • (1) bottle of clear dish soap
  • (1) bottle of blue food coloring
  • (1) small container of table salt (1 tablespoon)
  • (1) bottle of 70% isopropyl alcohol (100 ml)
  • (2) clear drinking cups (large enough to hold the 500 ml of water)
  • (1) tablespoon

Advisor Note

Make sure you add time in your activities for viewing and discussing videos with the Explorers. These videos are currently not built into the session plan so you will need to choose those that best complement your activities and plans for this topic.

 

Text in italics should be read aloud to participants. As you engage your post in activities each week, please include comments, discussions, and feedback to the group relating to Character, Leadership, and Ethics. These are important attributes that make a difference in the success of youth in the workplace and in life.

Activity 1

COLLECTING DNA EVIDENCE

Show Explorers the following video: “How to Properly Swab DNA Evidence at a Crime Scene” (National Forensic Academy)—www.youtube.com/watch?v=2HPeZWGtjD0.

 

Then have each Explorer follow this procedure:

  • Put on a pair of protective gloves.
  • Place a couple of drops of blood or a reddish-brown liquid or substance that has a consistency similar to blood onto a surface such as a countertop or onto an object such as a pencil and allow it to dry.
  • Moisten a cotton swab with a drop or two of water and rub it on the edge of the stain until a visible transfer has taken place; do not consume the entire evidence sample.
  • Take a second swab and swab the inside of the cheek of another Explorer; this is called a buccal swab and this is what is used to compare the DNA from a suspect to the DNA extracted from an evidence stain (blood, semen, saliva, etc.).
  • Dispose of the swabs and clean the bloodstain from the surface or object that it was deposited on.

Activity 2

EXTRACTING DNA FROM CHEEK CELLS

Show Explorers the following video: “Extract Your Own DNA” (PBS/NOVA)—www.youtube.com/watch?v=DaaRrR-ZHP4. Then have Explorers complete all of the steps as directed in the video.

Activity 4

CASE STUDIES

Show the Medical Detectives and/or the Forensic Files episodes listed under “Videos” to the Explorers and discuss how DNA evidence helped in the investigation.

Activity 5

SPEAKER OR VISIT

If possible, make arrangements for one of the following activities in order to provide Explorers with a real-world look at the profession of forensic science.

  • Arrange for a visit to a local, county, or state crime laboratory with an emphasis on the forensic DNA section.
  • Research cases in the media and on the internet that involve DNA evidence.
  • Attend a trial where DNA evidence is being presented.

Reflection

  • What is DNA and how is it passed from one generation to the next?
  • Explain the concept of base pairing as it pertains to DNA.
  • List at least three sources of DNA that can be useful in a criminal investigation.
  • Describe the steps used in forensic DNA analysis.
  • Should everybody who is arrested be required to give a DNA sample along with their fingerprints? Why or why not?
  • Do you think that DNA information stored in government database such as CODIS and NDIS could be misused? If so, how?

Advisor and Officer review

After the meeting, address the following:

  • Identify what was successful about the meeting.
  • Identify what needed improvement.
  • Schedule an officer and Advisor planning meeting to prepare for the next post meeting or activity.

 

All content is copyright Christopher Bily, Next Generation Forensic Science Initiative, West Virginia University. Used with permission.

 

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FORENSIC DNA ACTIVITY GUIDE
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