DNA Fingerprint: Sequences Assemble to Reveal Missing Links

 by Ronald Fritz Peril | Ikirara

On April 25 1953, scientists James Watson and Francis Crick stunned the scientific community with their three-dimensional model of the double helix structure of the DNA, a rather peculiar molecule at that time, which was published in Nature. But unknown to many people is the bedrock of scientific works laid out by other scientists that led to this discovery. Among them are Maurice Wilkins and Rosalind Franklin for the X-ray diffraction photograph of DNA and Erwin Chargaff, Emil Fischer, and Rollin Hotchkiss for the equimolar quantitative relationship of purines and pyrimidines.

The elucidation of the DNA structure is indeed a puzzle that scientists from diverse backgrounds worked on until the structure was completed. Since 1953, research efforts for understanding better the genetic material and its applications to society has been unstoppable.

One of the most prominent applications of DNA is in the field of Forensic Science, specifically DNA fingerprinting which is a molecular technique used to identify a person based on the nucleotide sequences found at specific regions of the DNA that are unique to every individual.

DNA sounds all too familiar, but what is it exactly? It stands for deoxyribonucleic acid, an information biomolecule found in all of your cells! It contains four compounds known as nucleotides or bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These only couple with specific pairs, such as A to T and C to G. There are approximately 3 billion of these pairs in your DNA, and the way they are formed together determines your traits and characteristics.

The genome is the complete set of DNA found in a cell. But wait! Aren't we all the same? That is without a doubt! However, our genomes are only 99.9% similar; the remainder serves as the factor that distinguishes us from one another, such as how we look, think, and feel! That remainder, it appears, was not revealed to us until 1984, when Professor Sir Alec Jeffreys had a eureka moment when he discovered and detected highly variable sequences in our genome, called minisatellites, and proposed its utilization in Forensic Genetics. The variable number of tandem repeats (VNTR) is used for DNA fingerprint analysis.

Let us now get into the specifics of DNA fingerprinting. If you want to compare your DNA fingerprint to that of your mother and father, you must collect cells from their bodies, as well as yours. To extract DNA from samples such as hair, saliva, semen, blood, and so on, you treat them with chemicals. After extracting the DNA, you use a restriction enzyme to cut the portion of the DNA into smaller segments where there is high variability between you and your parents. Then, pass an electric current through a gel to separate the small and large DNA fragments, and don't forget to add a dye to make them visible to an ultraviolet light or a laser. The end result will be a pattern of DNA bands that looks similar to a bar code in a supermarket you could compare to that of your parents.

Jeffrey's DNA fingerprinting method has high recognition accuracy, but its main limitations were being time-consuming and requiring at least 10-25 ng of DNA to be accurate. With these disadvantages, Restriction Fragment Length Polymorphism  (RFLP) is selectively used for forensic cases. Short Tandem Repeat (STR) analysis is the current benchmark for human DNA fingerprinting due to its accuracy and convenience.

An example of the use of DNA fingerprinting was highlighted in a tragic incident that occurred in which a woman was raped and killed. The authorities announced a major manhunt to locate the DNA profile that matches the killer's sperm. Approximately 500 specimens were gathered in the vicinity of the event. The DNA profiling had left the public extremely disappointed, seeing as it was unable to identify the killer. Fortunately, 6 months after the initial investigation, a woman testified that she overheard a man giving his blood for the sake of his colleague, Colin Pitchfork. Pitchfork's DNA was examined and confirmed. It turned out that it matched the killer's DNA. With its sophisticated technology, DNA fingerprinting stunned the entire world.

In hospitals around the world, DNA fingerprinting is used to diagnose inherited disorders in both prenatal and newborn babies. Hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, and other disorders are examples. Early detection of such disorders allows medical personnel and parents to prepare for proper treatment of the child. Genetic counselors also use DNA fingerprint information to help prospective parents to understand the risk of conceiving a child at risk of a genetic disorder. In other programs, expectant mothers make decisions about affected pregnancies based on DNA fingerprint information.

DNA fingerprinting, like all technologies, has limitations and should be improved to ensure accuracy. One example is DNA contamination, which hinders a DNA fingerprint from being used as evidence in court due to inaccurate results. Furthermore, the authority has the ability to manipulate the results, which is why replication in different testing labs is recommended. To be useful in criminal investigations, these methodologies must adhere to legal standards such as the Frye or Daubert Standards, which determine whether the evidence is admissible in court.