SUMMER RESEARCH PROGRAM FOR SCIENCE TEACHERS
ADRIENNE RUBIN
HIGH SCHOOL FOR THE HUMANITIES
LESSON PLAN
| “WHO DONE IT?” ANALYSIS OF MOLECULAR FINGERPRINTS LEFT AT THE SCENE OF THE CRIME |
BACKGROUND
Science has added a weapon to the crime lab’s arsenal. From a drop of blood, strands of hair, or other biological material left at the crime scene, scientists can provide a much better “fingerprint”, namely DNA. [9-12 Content Standard E- Understandings about science and technology]
To produce a DNA fingerprint, scientists isolate DNA from the blood or other organic evidence found at the scene of a crime. They will isolate DNA from the suspect. Blood samples are treated with enzymes that will cut the DNA into small fragments. [9-12 Content Standard C- The Cell] The length of these fragments depends on the sequence of nitrogenous bases-which differs from person to person.
The DNA fragments in samples from the suspect(s) and crime scene are subjected to gel electrophoresis. [9-12 Content Standard E- Understandings about science and technology] The DNA produced by each sample creates a series of bands. If the patterns match, a suspect can be connected to the crime or absolved of guilt. In fact, many prison inmates, some sitting on death row, have been cleared of wrongdoing when older investigations have been reopened and examined with the new technology.
THE CRIME
Nicki Green Simmons, a young and beautiful actress, has been murdered outside her condo in Hollywood. Her dog Bruno barked continuously until neighbors called the police and found her body. She had been stabbed repeatedly. She was recently divorced from her jealous and sometimes violent athlete husband J. T. Brown. He had been seen at her home on several occasions confronting her dates.
Kerry Adams, J.T.’s new girlfriend was jealous of Nicki and suspected J.T. was still in love with his ex-wife. Kerry was overheard in a restaurant expressing how she wished Nicki was out of the picture permanently.
Blood samples have been taken from Kerry and J.T. for DNA fingerprinting. DNA from blood at the crime scene will be compared from DNA taken from Kerry and J.T.
To compare their DNA, it must be cut into smaller fragments with restriction enzymes EcoR1 and Hind111.
OBJECTIVES
In this activity you will:
Digest DNA fragments using different restriction enzymes
Use a micropipette
Loan an electrophoresis gel
Run a gel and analyze the results [Teaching Standard D- Make accessible science tools]
MATERIALS
Electrophoresis Buffer
Electrophoresis chamber
Agarose gel
Micropipettes and tips
DC power supply
Loading dye
Crime scene DNA cut with EcoR1
Crime scene DNA cut with Hind111
Kerry Adams’ DNA cut with EcoR1
Kerry Adams’ DNA cut with Hind111
KT’s DNA cut with EcoR1
KT’s DNA cut with Hind111
Transilluminator camera
Gloves
Methylene Blue
PROCEDURE
Place the agarose gel in its gel bed in the electrophoresis gel chamber.
Add enough electrophoresis buffer to the gel chamber to completely cover the gel.
With a clean pipette, place 5ul of Kerry Adams’ DNA cut with EcoR1 into the first well in the gel.
With a clean pipette, place 5ul of Kerry Adams’ DNA cut with Hind111 into the second well in the gel.
With a clean pipette, place 5ul of KT’s DNA cut with EcoR1 into the third well.
With a clean pipette, place 5ul of KT’s DNA cut with Hind111 into the fourth well.
With a clean pipette, place 5ul of crime scene blood cut with EcoR1 into the fifth well.
With a clean pipette, place 5ul of crime scene blood cut with Hind111 into the sixth well.
Place the top on the gel chamber and connect it to a power supply. Plug in the power supply and adjust it to 75 volts. Run the gel until the samples have crossed the gel.
Turn off the power supply and slide the gel from the gel bed into an aluminum pie plate.
Cover the gel with methylene blue dye. Leave gel in dye for 10 minutes or until blue bands of DNA appears on the gel.
Pour Methylene blue into a stock bottle, and then rinse the gel in water several times.
Place the gel in the transilluminator camera and photograph your gel.
Compare the samples. You are looking for a match.
Why did you change your pipette tip each time you extracted each sample? [Teaching Standard B- Orchestrate scientific discourse]
_________________________________________________________
QUESTIONS
According to your data, whose blood was found at the scene of the crime? How do you know? __________________________________________________________
___________________________________________________________________
[9-12 Content Standard A- Formulate explanations using evidence]
Compare all the samples cut with EcoR1. __________________________________
___________________________________________________________________
____________________________________________________________________
Explain how the fingerprints on our fingers are a phenotypic trait while DNA typing analyzes genomic information? ____________________________________________
_____________________________________________________________________
[9-12 Content Standard C- The molecular basis of heredity]
Why is DNA fingerprinting more reliable than blood typing in identity cases? _______
Give other examples of organic evidence that may be used to extract DNA____________________________________________________________________
Besides paternity suits and crime scene analysis, what other situations can use DNA analysis? ____________________________________________________________________
[9-12 Content Standard F- Science and technology in local, national, and global challenges]
REFERENCES
Kreuzer,Helen and Adrianne Massey. 1996. Recombinant DNA and Biotechnology. A Guide for Teachers. ASM Press. Washington, D.C.
Micklos, David A. and Greg A. Freyer. 1990. DNA Science. A First Course in Recombinant DNA. Cold Spring Harbor Press. New York.
Schraer,William D. and Herbert J. Stoltze. 1995. Biology. The Study of Life. Prentice Hall. Massachusetts.
Walker, Pam and Elaine Wood. 1998. Crime Scene Investigations. Real Life Science Labs. The Center for Applied Research in Education. New York. [Teaching Standard D- Make accessible science media]