DNA Fingerprinting

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DNA Fingerprinting

DNA Fingerprints, RFLPs, Slot Blots -- these are all variants of the powerful new technology that has revolutionized forensic science: DNA testing. From identifying the remains of American soldiers, to deciding paternity cases, to eliminating -- and often convicting -- criminal suspects, DNA testing has become a powerful new weapon in the lawyer's arsenal.

First developed in England in 1985, DNA testing takes advantage of the fact that, with the exception of identical twins, the genetic material -- DNA -- of each person is unique. When the National Research Council said in a 1992 study that DNA testing was a reliable method to identify criminal suspects, the technology rapidly entered the mainstream court system. Today, it is hard to pick up a daily paper and not find an article reporting on the use of DNA testing in a civil or criminal court case.

The two animated tutorials below review the science and applications of DNA testing. To view each, simply click on the tutorial's link, and a new window will open on your screen. When you are finished with the tutorial, close your window and return here, where you can access the additional Internet resources listed below.

Basics of DNA Fingerprinting

By Kate Brinton and Kim-An Lieberman

This page was created as a class project at the University of Washington to provide to the Internet basic information on the structure and function of DNA as it relates to DNA fingerprinting. This topic is especially pertinent in today's society because of the rising use of DNA fingerprinting as evidence in court cases.

Animations

Note: you must have the Shockwave Plug-in to view this page's animations in your web browser.

DNA Fingerprinting via Southern Blotting PLAY

DNA Detective PLAY

Additional DNA Testing Internet Resources

Please note that these links are not part of the DNA Learning Center, and Cold Spring Harbor Laboratory has no control over their content or availability.

DNA Goes to Court, by Lynn Elwell, PhD.: An article on the use of DNA Testing in the courts, published in Carolina Biological Supply Company's Carolina Tips magazine, October, 1995.
DNA Fingerprinting (Microsoft Encarta Online entry): A concise definition of DNA Fingerprinting from the Microsoft Encarta Online encyclopedia.
How scientists and forensic experts use technology to analyze evidence from crime scenes: From the University of Wisconsin�s Why Files, an article about forensic science, and why DNA testing has become the main tool of lawyers and entomologists alike.
Use of DNA in Identification: Included in the MIT Biology Hypertextbook, an excerpt from a talk given by noted DNA researcher Dr. Eric S. Lander at the "Winding Your Way through DNA" symposium, which took place at the University of California San Francisco in 1992.

DNA Fingerprinting in Human Health and Society

Written by David F. Betsch, Ph.D., Biotechnology Training Programs, Inc.
Edited by Glenda D. Webber, Iowa State University Office of Biotechnology.
Obtained via Genentech's Access Excellence

Like the fingerprints that came into use by detectives and police labs during the 1930s, each person has a unique DNA fingerprint. Unlike a conventional fingerprint that occurs only on the fingertips and can be altered by surgery, a DNA fingerprint is the same for every cell, tissue, and organ of a person. It cannot be altered by any known treatment. Consequently, DNA fingerprinting is rapidly becoming the primary method for identifying and distinguishing among individual human beings.

An additional application of DNA fingerprint technology is the diagnosis of inherited disorders in adults, children, and unborn babies. The technology is so powerful that even the blood-stained clothing from Abraham Lincoln has been analyzed for evidence of a genetic disorder called Marfan's Syndrome.

The Structure of DNA

Living organisms that look different or have different characteristics also have different DNA sequences. The more varied the organisms, the more varied the DNA sequences. DNA fingerprinting is a very quick way to compare the DNA sequences of any two living organisms.

Making DNA Fingerprints

DNA fingerprinting is a laboratory procedure that requires six steps:

	1: Isolation of DNA. DNA must be recovered from the cells or tissues of the body. Only a small amount of tissue - like blood, hair, or skin - is needed. For example, the amount of DNA found at the root of one hair is usually sufficient.
	2: Cutting, sizing, and sorting. Special enzymes called restriction enzymes are used to cut the DNA at specific places. For example, an enzyme called EcoR1, found in bacteria, will cut DNA only when the sequence GAATTC occurs. The DNA pieces are sorted according to size by a sieving technique called electrophoresis. The DNA pieces are passed through a gel made from seaweed agarose (a jelly-like product made from seaweed). This technique is the biotechnology equivalent of screening sand through progressively finer mesh screens to determine particle sizes.
	3: Transfer of DNA to nylon. The distribution of DNA pieces is transferred to a nylon sheet by placing the sheet on the gel and soaking them overnight.
	4-5: Probing. Adding radioactive or colored probes to the nylon sheet produces a pattern called the DNA fingerprint. Each probe typically sticks in only one or two specific places on the nylon sheet.
	6: DNA fingerprint. The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously. It resembles the bar codes used by grocery store scanners.

Uses of DNA Fingerprints

DNA fingerprints are useful in several applications of human health care research, as well as in the justice system.

Diagnosis of Inherited Disorders

DNA fingerprinting is used to diagnose inherited disorders in both prenatal and newborn babies in hospitals around the world. These disorders may include cystic fibrosis, hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, thalassemia, and many others.

Early detection of such disorders enables the medical staff to prepare themselves and the parents for proper treatment of the child. In some programs, genetic counselors use DNA fingerprint information to help prospective parents understand the risk of having an affected child. In other programs, prospective parents use DNA fingerprint information in their decisions concerning affected pregnancies.

Developing Cures for Inherited Disorders

Research programs to locate inherited disorders on the chromosomes depend on the information contained in DNA fingerprints. By studying the DNA fingerprints of relatives who have a history of some particular disorder, or by comparing large groups of people with and without the disorder, it is possible to identify DNA patterns associated with the disease in question. This work is a necessary first step in designing an eventual genetic cure for these disorders.

Biological Evidence

FBI and police labs around the U.S. have begun to use DNA fingerprints to link suspects to biological evidence - blood or semen stains, hair, or items of clothing - found at the scene of a crime. Since 1987, hundreds of cases have been decided with the assistance of DNA fingerprint evidence.

Another important use of DNA fingerprints in the court system is to establish paternity in custody and child support litigation. In these applications, DNA fingerprints bring an unprecedented, nearly perfect accuracy to the determination.

Personal Identification

Because every organ or tissue of an individual contains the same DNA fingerprint, the U.S. armed services have just begun a program to collect DNA fingerprints from all personnel for use later, in case they are needed to identify casualties or persons missing in action. The DNA method will be far superior to the dogtags, dental records, and blood typing strategies currently in use.

For Further Reading

"DNA fingerprints witness for the prosecution." Discover. June 1988, p. 44.

DNA Identity Testing Information Package. Available from LifeCodes, Inc., Stamford, Connecticut. Phone toll-free: 1 (800) 543-3263.

Genetic Witness -- Forensic Uses of DNA Tests. U.S. Office of Technology Assessment. July 1990. Phone: (202) 224-8996.

"Molecular advances in genetic disease." Science. May 8, 1992.

"The promise and pitfalls of molecular genetics." Science. July 10, 1992.

Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and Cooperative Extension Services of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.

June, 1994