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, for example, even the blood-stained clothing of Abraham Lincoln could be analyzed for evidence of a genetic disorder called Marfan's Syndrome
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.
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.
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.
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.