Since Watson and Crick’s discovery of the double helix structure of DNA in 1953, biotechnology has advanced by leaps and bounds. DNA fingerprinting technology has built on achievements such as restriction enzymes and genetic code decoding, and has become an important tool in criminal investigations and personal identification. RFLPs and STRs analyses have increased the accuracy and reliability of DNA fingerprinting and have contributed significantly to criminal apprehension.
Since Watson and Crick’s discovery of the double helix structure of DNA in 1953, biotechnology has progressed at a remarkable pace. This was followed by the discovery of restriction enzymes, the decoding of the genetic code, and the development of a technique called DNA fingerprinting. Recently, DNA fingerprints have been used to identify the body of Yoo Byung-un and have helped to catch criminals in many crimes, but what is a DNA fingerprint and how can it identify an individual?
The development of DNA fingerprinting represents another revolutionary advance in biotechnology. This technology is not just limited to biological research, but can be applied in a variety of fields, including forensics, personal identification, and disease diagnosis. In forensic science, DNA fingerprints are used as conclusive evidence and play an important role in solving crimes.
The concept of DNA fingerprinting is based on the fact that just as fingerprints are different from one person to another, DNA is also different from one person to another. DNA is a structure of two complementary chains, called nucleotides, which are the basic building blocks of DNA. There are four types of nucleotides, depending on the bases that comprise them. A base is a ring of nitrogen and is the site where the complementary bonds mentioned above occur.
Like fingerprints, DNA fingerprints contain genetic information that is unique to each individual, and by analyzing the differences, it is possible to accurately identify a specific person. This can be used for a variety of purposes, including identifying missing persons, paternity testing, and diagnosing genetic diseases, and in recent years, the technology has become more sophisticated and reliable.
RFLPs (Restriction Fragment Length Polymorphisms) have been proposed to analyze these DNA fingerprints. On average, the DNA of two different people differs by one difference per 1,000 nucleotides, and these differences are called loci. RFLPs are a way to identify individuals by comparing multiple loci. However, it is not practical to compare these long nucleotide chains one by one, so an indirect method is used. This method is divided into three steps, the first of which is to cut the DNA chain using restriction enzymes. Restriction enzymes are responsible for recognizing specific sequences of bases and then breaking the bonds within the sequence. For example, the restriction enzyme EcoR I recognizes the sequence GAATTC and breaks the bond between the nucleotides with G and A. Since the sequences of DNA from two different people differ, the lengths of the DNA chain fragments cut by restriction enzymes will also differ. The second step is to arrange these fragments, which is done by applying a constant voltage to the gel while the DNA fragments are in the gel. Since DNA is negatively charged, it is electrostatically attracted to move from the cathode to the anode, and the degree of movement depends on the mass of the fragments. Finally, radioactive isotopes are used to identify specific DNA fragments. Radioisotopes are chemical elements that are unstable due to their large mass, and they release energy in the form of waves in order to stabilize. Add the DNA fragments synthesized to contain the radioisotope so that they complementarily bind and attach to some of the DNA fragments added in the second step. When the synthesized DNA fragments and the combined DNA fragments are exposed to X-rays, the radioactive isotopes cause them to exhibit color, and the individuals can be identified by comparing the colored fragments.
While RFLPs are highly accurate, they require intact DNA samples of 25 ng (n=10-9) or more, making them very difficult to use at crime scenes. At best, you might find a hair or a drop of blood at a crime scene, which is less than 1 ng of DNA. Furthermore, after some time, the DNA in these clues degrades and becomes corrupted, making it unusable for RFLPs.
These limitations were one of the major problems with early DNA analysis technologies, but advances in technology have helped to overcome them. New technologies have made it possible to produce reliable results with smaller samples.
STRs comparison with PCR has been proposed as a solution to this problem. PCR stands for Polymerase Chain Reaction. It uses DNA polymerase enzymes involved in the synthesis of DNA chains to replicate a sample of DNA, and an amplified sample of DNA can be obtained from an adapted amount of DNA. PCR technology cannot be used on samples for RFLPs because it can only replicate a maximum of 1,000 to 2,000 nucleotides. Therefore, on average, there will only be one or two RFLP loci, which is too few to identify the culprit among several suspects.
As a solution, Thomas Caskey proposed using DNA sequences called STRs to identify individuals. STRs (Short Tandem Repeats) are short sequences that repeat at specific locations on DNA chromosomes. Since each individual has a different number of repeats, the signals from different fragments of STRs can be combined to identify an individual. In real-world criminal investigations, 13 types of STRs are used, each consisting of four sequences standardized by CODIS in 1998. Because STRs are short chains, they can be replicated using PCR. During the PCR process, specific nucleotides are incorporated into the cloned DNA. These specific nucleotides absorb specific bands of light, and when a laser is shone on them, they show a specific color. Then, as with RFLPs, the different pieces of STRs are placed in a gel and applied with voltage. By detecting and comparing the differently colored signals from the lasers, individuals can be identified. STRs analysis is so accurate that the probability of two different people having the same STRs signal is as low as 1 in 10^18.
The introduction of STRs analysis has revolutionized criminal investigations. It hasn’t just increased accuracy and reliability, it has also made it possible to extract meaningful information from microscopic evidence found at crime scenes. This has led to a significant increase in crime solving rates and has played an important role in exonerating wrongfully accused people.
In this article, we have compared two DNA fingerprinting methods, RFLPs and STRs combined with PCR. In the modern world, where felonies are becoming more sophisticated and varied in their methods, it is important not to miss even the smallest clues, as they can be the key to catching a criminal. It is clear that STRs will continue to be widely used in criminal investigations thanks to their high sensitivity and accuracy, two characteristics that allow them to identify individuals even with small amounts of DNA samples.
Therefore, DNA fingerprinting technology is expected to play an even more important role in future criminal investigations. With the continued advancement of the technology, DNA analysis will become more accurate and reliable, which will contribute to a safer and more just environment for society as a whole.
