DNA Fingerprinting: You Be The Judge!

Carolyn Napier Martin
1992 Woodrow Wilson Biology Institute


Rationale:

DNA fingerprinting has been hailed as the greatest advance in forensic science since traditional fingerprinting, but it is feared by some that this powerful tool has been accepted into the courts before all the " kinks" have been worked out. These activities allow the student to understand the con-cepts and the problems.

Intended Audience:

Biology I and II students who have an understanding of DNA structure and function, restriction enzymes and gel electrophoresis. An introduction to these activities should include a lab or simulation lab on DNA fingerprinting (perhaps using EDVOTEK Kit 109 - EDVOTEK, P.O. Box 1232, West Bethesda, MD 20817; 800-EDVOTEK)

Objectives:

The students will use their knowledge of DNA fingerprinting to evaluate use of certain prints in courts and will address the ethics of establishing a national database of fingerprints.

Materials:

  • Selected Articles (See Bibliography)
  • Copies for each student of:
  • Student Procedure and Background
  • Photographs of DNA Fingerprints
  • An Ethical Decision Making Model From Front of Module

Procedure:

Review how DNA fingerprinting is done, if needed, and have students read the background information. It will be helpful to have copies of some of the articles on the controversy of DNA fingerprinting for student reference. The OTA book, Genetic Witness: Forensic Uses of DNA Tests has very good background material. This may be ordered from: Superintendent of Documents; Government Printing Office; Washington, D.C. 20402-9325; GPO Stock number 052-003-01203-1; price $9.50; ordering info: 202-783-3238.

Students may work alone or in small groups to carry out the activities. For the ethical decision making model, follow the suggested protocol.

References:

Chakraborty, Ranajit , and Kidd, Kenneth E., "The Utility of DNA Typing in Forensic Work," Science 254:1735-1739, 1991.

Devlin, B., Neil Risch, and Roeder, Kathryn, "Forensic DNA Test and Hardy-Weinberg Equilibrium," Science 253:1037-1041, 1991.

Lewis, Ricki, "DNA Fingerprints: Witness for the Prosecution," Discover 9:44-51, 1988.

Lewontin, R. C., and Hart, D. L., "Population Genetics in Forensic DNA Typing," Science 254:1745-1750, 1991.

Norman, Colin, "Maine Case Deals Blow to DNA Fingerprinting," Science 246:1556-1558, 1989.

Rasmussen, Alison M., and Matheson, Robert H., A Sourcebook of Biotechnology Activities, National Association of Biology Teachers and North Carolina Biotechnology Center, 1990.

Risch, Neil S., and Devlin, B., "On the Probability of Matching DNA Fingerprints," Science 255:717-720, 1992.

Roberts, Leslie, "Fight Erupts Over DNA Fingerprinting," Science 254:1721-1723, 1991.

Roberts, Leslie, "DNA Fingerprinting: Academy Reports," Science 255:300-302, 1992.

Congress, Office of Technology Assessment, Genetic Witness: Forensic Uses of DNA Tests, U.S. Government Printing Office, Washington, D.C., 1990.


Student Worksheet

Name ____________________________

Period ____________________________

DNA FINGERPRINTING: YOU BE THE JUDGE!

You should read the background information below so that you will have the knowledge required to judge the validity of the DNA fingerprints shown on the last page of this exercise. You may also need to read some of the articles which your teacher has on DNA typing or to do some reading in the library.

Background Information:

DNA fingerprinting is a technique that is used to collar criminals, exonerate innocent persons, and identify fathers in paternity cases. Courts around the world have admitted DNA fingerprinting as evidence in hundreds of murder, rape, and paternity cases. DNA isolated from blood, semen, hair, tissue, bone marrow, saliva, and urine left at the scene of a crime may identify an assailant. The U.S. Armed Forces began with new recruits in June, 1992 to collect DNA samples which will be used to identify fallen service personnel and will eventually include all military persons.

For several years now, leading scientists have waged heated courtroom battles over the reliability of DNA fingerprinting. The major problems are:

  1. Reliability of Population Data

    The probability of finding a match for a particular DNA pattern is found by multiplying the probability of the separate loci in a particular reference population. The FBI has developed a database of population statistics for Caucasians, Blacks, Hispanics and Asians. The problem is that there is much variability within each of these groups. (Asians include Chinese, Japanese and Koreans, for example.) While the probability of finding a match in the reference population may be very small, (e.g. 1 in 6 million) it could be much more likely (e.g. 1 in 800,000) if only the smaller subgroup were used.

  2. Determining a Match

    This becomes difficult when there are only small differences in the number of variable number tandem repeats at a particular locus. Problems are also caused because of "band shifting" which may occur with differences in the gel or excess DNA in a well.

  3. Contamination and Degradation of DNA Samples.

    Samples may be contaminated because of bacterial growth in the sample before it was collected. Old samples may also break down and give inadmissible results. These samples may have extra bands or be missing bands.

  4. Quality Control Practices of Labs

    Presently there are no standards for labs nor any kind of licensing of labs. This may lead to poor test quality.


Procedure: Activity A.

Your job is to evaluate the copies of the photographs of some DNA fingerprints (last page of exercise) from the files of the FBI and from Cellmark Diagnostics, a DNA fingerprinting lab. Your group will examine each sample and make certain decisions concerning the print.


dna print

Look at Print 1, which shows DNA from a rape victim (known female) in lane 3 and a suspect male in lane 4. Lane 6 shows semen recovered from the rape victim. The suspect is a recent Cuban immigrant, so the Hispanic database was used to determine the probability of there being another person with the same print.

Should this evidence be used in court? ____

Give your reasons:  _______________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________






Look at Print 2, which was made in preparation for a murder case. M = marker; K562 = standard; K1 = DNA from the suspect; Q 1-6 = DNA from hair found clutched in the victim's hand. In Print A, the well containing DNA from the suspect was overfilled. What phenomenon has occurred?

___________________________________________________________________________

Should this evidence be used into court? ____




Look at fingerprint B. Two wells were filled with the suspect's DNA. Q3 contains evidence from the crime scene. Should this second set of prints be used in court?

___________________________________________________________________________

Why or why not?  __________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________





Print 3 shows DNA from two paternity cases. Use the following key to identify the lanes:

M1 = First MotherM2 = Second Mother
C1 = First ChildC2a = Second Child
AF1 = Alleged FatherC2b = Third Child

AF2 = Alleged Father 2

Is AF1 the father of C1? ____

Is AF2 the father of C2a? ____ C2b? ____

Do you think that the quality of these prints good enough for court evidence?

___________________________________________________________________________

Procedure: Activity B

Read the article "DNA Fingerprinting: Academy Reports," Science, April 17, 1992 and answer the following questions:

What recommendations has the National Academy of Science made relative to population substructure and the calculation of chance of a match between the DNA patterns of a suspect and another person?

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

How will this affect the impact of DNA fingerprint evidence in court?

________________________________________________________________________

________________________________________________________________________

Procedure: Activity C

Because many convicted sex offenders repeat their crimes, some states have enacted laws requiring that their DNA be kept on file as an aid to solving future crimes. It has also been proposed that a national database of DNA fingerprints be set up, including those of job applicants and all newborns.

Use one of the ethical decision-making models at the front of the module to resolve this question.


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