DNA Fingerprinting Methods

Up through 1984, the only method of establishing and authenticating personal identification was by the fingerprint process. Since no two humans have been found to have identical pattern of ridges on their fingers, this method has been universally accepted as a means of personal identification. What if you are looking for a set of fingerprints that have not been classified and put into the world wide computerized system for fingerprint identification? In 1984, Sir Alec Jeffreys at the University of Leicester in England was able to distinguish differences among individuals based solely on their DNA composition. Since this advancement in forensic science was announced in 1985, there has been tremendous progress made in the methodology of extracting the DNA samples from such things as blood, saliva, personal items and in the identification of human remains.

The main types of DNA fingerprinting methods in use at this time are:

Restriction fragment length polymorphism (RFLP) analyzes the length of the strands of the DNA molecules with repeating base pair patterns. DNA molecules are long strands found tightly wound in chromosomes which are contained in the nucleus of each human cell. Within each DNA strand are numbers of genes that determine the particular characteristics of an individual. While about 5% of the gene compositions on DNA contain this type of genetic information, the other 95% do not. However, of the 95%, these non-coding genes contain identifiable repetitive sequences of base pairs, which are called Variable Number Tandem Repeats (VNTR). To extract a DNA fingerprint, a Southern blot is performed and the DNA is analyzed via a radioactive probe. The restriction fragment length polymorphism analysis is used to detect the repeated sequences by determining a specific pattern to the VNTR, which becomes the person's DNA fingerprint. The drawback with this system is that it requires a considerable amount of DNA in order to be used.

2. PCR
The polymerase chain reaction (PCR) was developed by Karry Mullis of the Cetus Corporation in 1983 for use in research laboratories for establishing hereditary authentication. The PCR analysis amplifies the DNA molecules using a smaller sample. On the forensic front, the PCR found to be useful in identifying DNA fingerprints in criminal matters and in paternity tests because it requires less amounts of DNA because it makes identical copies of the DNA sample. The PCR analysis amplified isolated regions on the strands of the DNA under examination. The drawback was that it was not as discriminating as the RFLP.

3. AmpFLP
Amplified fragment length polymorphism (AmpFLP) came into vogue in the 90's and is still popular in the smaller countries involved in the process of DNA fingerprinting. It remains attractive because of its relatively less complicated operation and the cost-effectiveness of the procedure. By using the PCR analysis to amplify the minisatellite loci of the human cell, this method proved quicker in recovery than the RFLP. However, due to the use of gel in its analysis phase, there are issues of bunching of the VTRN's, causing misidentifications in the process.

4. STR
The short tandem repeat (STR) methodology for extracting DNA is the system most widely used form of DNA fingerprinting. This system is based on the features of PCR, as it utilizes specific areas that have short sequential repeat DNA. The STR analyzes how many times base pairs repeat themselves on a particular location on a strand of DNA. The big advantage in this method is that the DNA comparisons can match the possibilities into an almost endless range.

DNA fingerprinting has been extremely successful for use in the personal identification of criminal suspects, DNA testing for ethnicity, identification of the deceased, as well as court-approved paternity tests. DNA, however, still poses issues because the VNTRs are not evenly distributed in all people because they are inherited. In addition, there is still the imperfect human element as the final voice in the administration of all DNA fingerprinting procedures. However as forensic scientists continue their research, there appears to be no limit to the value a DNA test can render to society.