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DNA Fingerprinting (Christian Sanchez)

Title: DNA FIngerprinting: Modeling Electrophoresis

Principle(s) Investigated: 

    DNA can be used as evidence to determine likely culprits of crimes. Since DNA is unique for every individual, it is very good evidence.

Standards : 

7th Grade Life Science Standards

1c: Students know the nucleus is the repository for genetic information in plant and animal cells.

2e: Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.


Lab book



Six (6) worksheets

  1. Half sheet definitions
  2. DNA fingerprinting scenario
  3. "Gel" worksheet to simulate electrophoresis
  4. DNA half sheet of suspects
  5. Sources of DNA sheet
  6. Additional questions for those who finish early

    Teacher will engage the students by claiming that the classroom pet (or anything else) has been stolen. The teacher will the let the students know that the burglar has left behind some DNA and that we are going to determine who stole the pet by comparing the DNA of 4 suspects with the DNA left at the crime scene. 
    As a class, go over the DNA fingerprinting scenario explaining key terms that the students may need help with; for example, electrophoresis. Explain to the students how electrophoresis works and that they will be modeling the process on their own. Do an example using using the crime scene DNA. Cut it at the appropriate areas and show them where it would go on the gel.Then allow the students to begin working.
    After the students have finished, discuss how we know who stole the pet.

Student prior knowledge
    Students should know that individuals DNA is unique, and because of that, we can match DNA found somewhere with the right person.

    The purpose of this experiment is to show students an example of how we can use DNA in practical ways. Given the popularity of crime shows on TV, it is bound to spark student interest. 
    We are modeling the process of electrophoresis using DNA found at the crime scene with DNA of 4 select students. Using actual students from the classroom gets them more involved in the assignment. It is important to know your students so you do not pick someone who would be offended. It may be best to ask for their approval. 
    We know that electrophoresis separates DNA according to size, with larger pieces staying closer to the negative end and smaller pieces moving closer to the positive end because of DNAs overall negative charge. 
    When we match all the DNA on the model gel, we can determine who the culprit is by seeing whose DNA matches with the crime scene DNA according to size.

Questions & Answers: 
    1. You recently found out that your father is one of three men, but your mother is not sure. How can you find out?
        Using the process we just learned, you would run the DNA of the 3 males along with yours and your mothers (each in a sepearte well on the gel). When you find the males DNA that when combined with your mothers matches yours, that is your father.
    2. There has been a burglary and the thief unknowingly left traces of DNA (let us hope he didn't bring someone elses along as bait). Can we determine the burglar?
        If we have suspects, we can at least run their DNA along with the crime scene DNA, and if theirs matches the crime scene DNA, then they are the culprit; if not, we can rule them out and move on.
    3. How can you determine who sexually assaulted a victim?
        If they left DNA behind, it is possible to match it with theirs to determine who the guilty party is. Run it through a gel like with the other examples.
Applications to Everyday Life:
As used in the questions:
    1. By using DNA to determine who the father or mother is of an offspring. Use electrophoresis and match the childs DNA with the two parents by comparing the peices of DNA. The child should have peices from the mother and father.
    2. If there is DNA at a crime scene, it can be ran through the gel in electrophoresis against the suspects. When there is a match, it is the likely culprit.
    3. When a victim is sexually assaulted, if DNA evidence is left behind, it can be used to determine who the assailant is and is not from a gorup of suspects. Simply run it through the gel against the suspects and wait for a match.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.