DNA FINGERPRINTING

INTRODUCTION

It is widely known that each individual has a DNA profile as unique as a fingerprint. Actually, over 99% of all 3 billion nucleotides in human DNA which we inherit from each parent are identical among all individuals. However, for every 1000 nucleotides that we inherit there is 1 site of variation or polymorphism, in the population. These DNA polymorphisms change the length of the DNA fragments produced by the digestion of restriction enzymes . The resulting fragments are called restriction fragments length polymorphisms (RFLP's--"riflips"). Gel electrophoresis can be used to separate and determine the size of the RFLPs. The exact number and size of fragments produced by a specific restriction enzyme digestion varies from individual to individual. DNA fingerprinting has proved valuable, not only for convicting felons and exonerating the innocent, but also for establishing maternity or paternity and proving family relationships. More exotic uses include the identification of missing children in Argentina, soldiers killed in war, and even the body of Nazi physician Joseph Mengele, the so-called "Angel of Death."

O.J.Simpson

BACKGROUND
An individual's DNA is as distinctive as a fingerprint. This technique was used to assist in determining O.J. Simpson's life. DNA samples can be obtained from the trace amounts of blood or seman. These DNA samples can be separated using gel electrophoresis. The number and position of bands formed on each lane of gel is the actual genetic "fingerprint" of that DNA sample. The characteristics of certain segments of DNA vary from person to person and form a highly individual, detectable "genetic fingerprint." Developed only in the mid-1980s, genetic fingerprinting has rapidly bacome a widely used courtroom tool. In 1988 the first person in the United States was executed based on DNA technology.

The beginnings...
The fundamental techniques involved in genetic fingerprinting were discovered serendipitously in 1984 by geneticist Alec J. Jeffreys of the University of Leicester in Great Britain while he was studying the gene for myoglobin, a protein that stores oxygen in muscle cells. He found that the myoglobin gene contains many segments that vary in size and composition from individual to individual and that have no apparent function. Jeffrey called these segments minisatellites because they were small and they surround the part of the gene that actually serves as a genetic bluprint. The minisatellites accountsfor less than 1 percent of hte total DNA of a human. Jeffreys isolated several of these minisatellite genes and inserted each into bacteria, which produced large amounts of the DNA segments. These segments could then be purified and labeled with radioactive isotopes to produce genetic probes that are the key tool in producing genetic fingerprints.

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STEP BY STEP

Steps to Producing a Genetic Fingerprint:

The first step is to obtain a sample of of DNA from such substances as blood, semen, hair roots, or saliva. Using newly developed biochemical techniques to multiply the amount of DNA present, researchers can work with as small a sample as one hair root.

The individual cells from the sample are split open, and the DNA is separated from the rest of the cellular debris.

The DNA is then treated with specilaized proteins called restriction enzymes, which cleave the DNA into smaller fragments by cutting at specific sites. Since the minisatellites from any two individuals have different compositions, they are cleaved at different sites, producing fragments of different lengths. The DNA fragments are then applied to one end of a thin, jellylike substance called an agarose gel, and an electric current is passed through the gel. The negatively charged DNA fragments will migrate across the surface of the gel in response to the current, with the smaller, more mobile pieces traveling farther. The DNA is thus separated into individual bands, with the fragments in each one progressively smaller in size.

Because the gel cannot be easily handled, a thin nylon membrane is laid over its surface and covered by a layer of paper towels. As the towels draw moisture from the gel, the DNA is transferred onto the surface of the nylon membrane, a process called blotting.

The DNA bands are still invisible to the eye, and there are too many to be useful. Therefore, a solution of the radioactive probes made from minisatellites is washed over the surface of the membrane. If any of the probes have the same composition as a part of a DNA fragment, they will bind to it. The probes will ingnore the vast majority of the hundreds of bands present and will bind anywhere from 6 to 20. To see the pattern of bands, the researchers place a sheet of photographic film on top of the membrane. The radioactive labels will expose the film, ultimately producing a pattern of thick-and-thin dark bands. This pattern of bars is the GENETIC FINGERPRINT. The entire process can require as long as four to six weeks in a commercial laboratory. But in November 1991, Jeffreys announced the development of a refined version of the test that allows results to be obtained much faster--in as little as two days.

APPLICATIONS

Varied Applications of DNA Fingerprinting The likelihood that two individuals--other than identical twins--will have the same genetic fingerprint varies from about one in 800,000 to about one in 1 billion, depending on the number of probes that are used in the test. By comparison, the probability that two individuals will have the same conventional fingerprint is also about one in 1 billion. But the genetic fingerprint has many other advantages over conventional fingerprints.

It is unusual for police to find a high-quality fingerprint at a crime scene, but much more likely that they will find blood or semen. Furthermore, only a microscopically small sample is required for a positive identification.

No relationship exists between the conventional fingerprints of parents and children, but the genetic fingerprints are closely related because the child receives half of her or his genetic information from each parent. Thus, half the bands int he child's genetic fingerprint come from the mother, and half from the father. This similarity can be used to establish paternity (or maternity) with a much higher degree of certainity than is possible with other techniques, such as a blood test.

Another application for this technique involves the effort to determine whether bones unearthed seven years ago in Argentina are those of Joseph Mengele, the chief physician at the Auschwitz concentration camp who supervised the systematic extermination of about 4 million Jewish men, women, and children during World War II. On behalf of the German government, Jeffreys extracted a small amount of DNA from one of the bones and compared it to DNA from Mengele's son, Rolf Jenckel, and Jenckel's mother. In April 1992, he reported that the bones were indeed Mengele's, finally closing the searchfor hte sadistic physician. Genetic relationships with grandparents can also be determined accurately. During the Argentine military's rule in the early 1980s, many government opponents were seized and killed, and their young children were given to military families or sold. After the military government was overthrown, activist Argentine groups began trying to locate the children and return them to grandparents of other family members. Genetic fingerprinting has played a key role in many successful reunions.

USES TODAY AND TOMMORROW
In January 1992, the U.S. Department of Defense announced that it plans to establish a database of genetic fingerprints and blood samples for all 1.5 million people in the armed forces. The data would be used to identify the remains of soldiers killed in action, thereby preventing the recurrence of any more "unknown soldiers."

Law enforcement officials have also talked extensively about the prospect of establishing a similar database of known sex offenders that would serve, like the FBI's fingerprint files, to aid in the identification of unknown assailants.

Genetic fingerprinting is not restricted to humans. Biologists routinely use it, particularly in their efforts to protect endangered species.

DNA Fingerprinting is used world wide and will not only continue to be, but also increase as an important factor in our daily lives.

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