Role Of Dna In Forensic Investigations Biology Essay

During the last 3 decennaries, DNA has risen to go one of the key tools for Forensic experts in work outing offense. The engineering was foremost applied to forensic scientific discipline in 1980 and since so, it has become a major turning country of research in the forensic universe ( 1 ) . This assignment will discourse the construction of DNA, the types of Deoxyribonucleic acid and what makes them so utile in forensic probes. Besides discussed are the assorted engineerings used for DNA profiling which depend on the features of the forensic instance itself. The assorted utilizations of DNA in forensic probes have besides been mentioned in this assignment along with the legal and ethical issues associated with DNA grounds.

Deoxyribonucleic acid stands for Deoxyribonucleic acid. In 1953, Watson and Crick proposed a dual coiling construction for DNA as shown in Figure 1 below. Each concatenation is made up of a phosphate anchor, deoxyribose sugar and four nitrogen-bearing bases: Adenine ( A ) , Guanine ( G ) , Thymine ( T ) and Cytosine ( C ) . ( 2 )

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Figure 1: Structure of DNA ( 3 )

From the above figure we can see that the two ironss run in opposite waies and the bases of these ironss are connected together by H bonds. Adenine is connected to Cytocine with two H bonds, while Guanine and Thymine are connected to each other by 3 H bonds ( 2 ) .

Types of Deoxyribonucleic acid

Nuclear Deoxyribonucleic acid

Nuclear DNA is located in our chromosomes which are stored in the karyon of each cell. Every single receives half figure of chromosomes from his/her female parent and the other half from the male parent ( 4 ) . This means that DNA is transferred from both parents to their progeny ‘s which makes it responsible for the transmittal of features and traits from one coevals to the following. Every human being has a alone transcript of their atomic Deoxyribonucleic acid, i.e. they do non portion the same DNA features with other worlds. The lone exclusion to this is in the instance of Identical twins where they have the same atomic Deoxyribonucleic acid, nevertheless it might differ in minor ways ( 4 ) .

Mitochondrial Deoxyribonucleic acid

Deoxyribonucleic acid is besides found in the chondriosome ‘s of cells, which are the power house of the cell. This is termed as Mitochondrial DNA or merely mtDNA. Unlike atomic Deoxyribonucleic acid, mitochondrial DNA is non alone to every person. It is inherited merely from the female parent and there are over 1000 transcripts in each cell ( 5 ) . This means that the mitochondrial DNA in an person would be the same mitochondrial Deoxyribonucleic acid found in the person ‘s female parent, maternal grandmas and siblings ( from the same female parent ) .

Why is Deoxyribonucleic acid used in Forensic Science?

Dr. Edmond Locard was one of the early innovators in the field of forensic scientific discipline. He proposed the ‘exchange rule ‘ which states that when two objects come into contact there is ever a transportation of stuff between them ( 6 ) . In the forensic scientific discipline universe, the stuff of involvement that is transferred at a offense scene is the wrongdoers DNA. It can be transferred onto the victim or onto a touchable object which makes it physical grounds. Physical grounds may include things such as glass, tools, pieces, missiles, vesture etc. Deoxyribonucleic acid can besides be extracted from any organic structure fluid such as blood, spit, perspiration, mucous secretion. It can besides be extracted from the fragments of a organic structure which included tegument, hair, bone etc ( 6 ) .

Once the Deoxyribonucleic acid is found at a offense scene, it is sent for analysis to find which person this DNA profile most likely belongs to. This procedure has many different names which include DNA fingerprinting, DNA typing or DNA profiling. The thought behind DNA fingerprinting is indistinguishable to the thought of standard fingerprinting. Every person has a alone set of finger prints and in the same manner ; every person has a alone DNA profile ( except indistinguishable twins ) . The lone difference is the fact that in DNA fingerprinting involves comparing DNA strands as seen in Figure 2 below. These characteristics make Deoxyribonucleic acid highly utile in forensic probes.

Figure 2: Deoxyribonucleic acid Fingerprinting ( 7 )

Deoxyribonucleic acid engineerings used in Forensic Science

There are assorted engineerings used in forensic scientific discipline to execute DNA profiling. The engineering used depends on the sum of DNA sample found at the offense scene, sum of debasement the Deoxyribonucleic acid has suffered and besides the type of instance that is under probe, i.e. whether it is a missing individuals instance, or a sexual assault instance etc.

Restriction Fragment Length Polymorphism ( RFLP )

Restriction Fragment Length Polymorphism involves the extraction of Deoxyribonucleic acid from blood or seeds samples. Figure 3 illustrates the assorted stairss involved in RFLP analysis.

Figure 3: RFLP procedure ( 8 )

The Deoxyribonucleic acid is cut into fragments which are placed onto an Agarose gel. They undergo a procedure called cataphoresis. This procedure separates the fragments based on their size since big fragments move slower than the smaller fragments. Once the fragments are separated they are placed on a nylon membrane for Southern Blotting. Short pieces of individual stranded radioactive DNA investigations bind to specific DNA fragments on the membrane which contain the complementary base sequences ( 9 ) . The membrane is so washed and processed against an X-ray movie to uncover the radioactive form. It is this Deoxyribonucleic acid form that is so compared to the DNA profiles of known persons.

It is extremely accurate and is chiefly used to know apart between multiple samples. Despite holding these qualities, RFLP has its draw dorsums every bit good. The technique is a long procedure, requires high measure and high quality DNA, i.e. degraded samples of Deoxyribonucleic acid can non be used. This technique used to be one of the criterions and is still used in DNA forensics ( 10 ) .

Polymerase Chain Reaction analysis ( PCR )

The Polymerase Chain reaction technique was developed in 1986 by Kary Mullis ( 10 ) . It consequences in the elaboration or duplicate of DNA. It gives forensic experts the power to bring forth more Deoxyribonucleic acid from the DNA grounds found at the offense scene. Hence, one of the major advantages of this technique is the fact that it can be done on little and debauched sums of DNA ( 6 ) .

The development of this technique was one of the major promotions in engineering used for DNA profiling. PCR improved the sensitiveness of analysis and it took significantly less clip as compared to the RFLP. It is besides more cost efficient as less labour is required ( 4 ) . This technique is really suited for bulk offense scenes because physical grounds such as individual hair strand, coffin nail buds, saliva hints etc contain merely little sums of Deoxyribonucleic acid. ( 11 )

Short Tandem Repeat analysis ( STR )

This technique is based on the Polymerase Chain Reaction. STRs are DNA parts with little repetition units. There is a batch of fluctuation in these repetition units which is why they exhibit a high grade of length polymorphism ( 12 ) . Because of this great fluctuation in STR repetitions between persons, it makes STR analysis an effectual technique in forensic scientific discipline for designation of worlds. Another advantage of this technique is the fact that degraded and low sums of Deoxyribonucleic acid can besides be typed with high truth ( 13 ) .

Mitochondrial DNA analysis

Mitochondrial DNA analysis is done in the instance of losing persons. This is because there is a high mutant rate between mtDNA which makes it extremely variable between unrelated persons. Due to its maternal heritage form, mtDNA from the female parent, grandma or siblings can be used to place victims. Besides, there are big figure of transcripts of mtDNA in each cell which means that it can be recovered from little, old and degraded samples ( 5 ) . Despite these advantages, mtDNA analysis is done in forensic probes merely if the atomic DNA analysis fails to demo positive consequences. This is because mtDNA posses some proficient and interpretational challenges ( 1 ) .

Y-Chromosome analysis

The Y chromosome is present in males merely and it consists of several familial markers which are of usage in forensic probes. Y-chromosome analysis is an first-class technique used to analyse biological grounds which has hints of multiple male subscribers. It can besides be used to track household relationships amongst males since male parents pass on their Yttrium chromosomes to their boies ( 7 ) .

Possible Outcomes of DNA profiling

Once the analysis of the DNA is complete utilizing these engineerings, it consequences in three possible results ( 14 ) .

Match: This indicates that that there is no unaccountable difference between the samples that have been compared.

Non-Match: This indicates that there be differences between the DNA profiles therefore proposing that the compared samples have different beginnings.

Inconclusive: This indicates that the consequences of DNA profiling do non corroborate a lucifer.

Uses of DNA in Forensic Science

Missing Persons

As mentioned in subdivisions 2.2.2 and 4.4, mtDNA is passed onto an person from the female parent. This means that mitochondrial Deoxyribonucleic acid from the female parent, maternal grandmas or even siblings can be analyzed to place persons. An illustration of where DNA analysis was done to place victims was after the 9/11 incident. The lone remains of most of the victims were castanetss and little tissue fragments. These samples were collected and a new information base of the 9/11 victims DNA profiles was made. These profiles were studied and analyzed which resulted in a bulk of victims being right identified ( 15 ) .

Burnt Victims

Deoxyribonucleic acid can besides be used to place burned victims. This is done utilizing Mitochondrial DNA because it has an advantage over atomic DNA as mtDNA can last rough environmental impacts such as Burnss, which atomic Deoxyribonucleic acid can non ( 4 ) . This makes mtDNA an first-class tool for Forensic experts to place burned victims. It has besides extensively been used in archeology and anthropology. A survey conducted in 2001 showed that mtDNA was successfully recovered from Pleistocene skeletal remains of Australian Aboriginal, putatively dating the skeleton beyond 60,000 old ages ( 16 ) .

Tracking Viral Transmissions

Another usage of Deoxyribonucleic acid in forensic probe is to track the transmittal of viruses from individual to individual. Transmission of bugs deliberately or negligently is an offense. Some of the familial viruses include Human Immunodeficiency Virus ( HIV ) . These can be tracked from sexual assault instances or even attempted manslaughter. But tracking these virus transmittals accurately is a challenge because viruses tend to germinate quickly and as a consequence their genome alterations rapidly over clip. Besides, the genetic sciences of the host has an impact on the diverseness of these virus strains. The methodological analysis to track these viruses from a sexual assault instance involves roll uping the samples from the male /female suspects and sequencing the HIV genome. This is compared to the HIV sequences of a control group from the same geographic country, which can find the relationship of virus strains ( 5 ) .

Forensic Entomology

Forensic Entomology involves the survey and usage of insects in forensic probes. It is used to gauge the clip of decease of a organic structure and to find if the cadaver was moved in anyhow. Traditionally, forensic experts use the morphological characteristics of the insects to find these inside informations. However, there are a figure of draw dorsums associated with morphological designation of specimens such as ; harm to specimens can impact their morphology ensuing in inaccurate consequences and the fact that rise uping is clip devouring ( 5 ) .

A survey conducted in 2002 was aimed at separating species utilizing DNA. The consequences of the survey suggest that mtDNA can be used to placing species in forensic bugology ( 17 ) . Using Deoxyribonucleic acid over morphological characteristics in forensic probes has many advantages which include that fact that Deoxyribonucleic acid can be extracted even if the specimens dice and it is a faster at placing than rise uping ( 5 ) .

Legal facet of DNA grounds

Even though DNA fingerprinting can place the individuals involved at a offense scene, DNA grounds can non be used to turn out that a individual has committed a certain offense. But DNA grounds can be used to turn over old serologically based guilty finding of facts because of its higher discriminatory power ( 10 ) .

Another legal issue relates to the developments of databanks which store Deoxyribonucleic acid from known felons. This can turn out to be really utile for future forensic probe because the Deoxyribonucleic acid found at offense scenes could be compared to the Deoxyribonucleic acid from the informations Bankss which would most likely place the felon. However this system is considered to be a colored system because Deoxyribonucleic acid from persons with no condemnable record is non collected. This implies that people with no condemnable records will non perpetrate any offenses in the hereafter, which is clearly non true ( 18 ) . This can take to ethical issues.

Occasionally, suspects challenge the forensic research lab in which the Deoxyribonucleic acid trials were done. They can impeach the lab of non following appropriate protocols and processs to accurately type samples. If this is proven to be true, so the Deoxyribonucleic acid grounds against the condemnable no longer holds and gives the suspect the chance for a 2nd trial by an independent research lab ( 11 )


Based on the stuff discussed above, it is clear that DNA is one of the biggest assets that forensic research workers have. It has a broad assortment of utilizations in forensic probes and a figure of DNA profiling techniques can be used depending on the quality and measure of the Deoxyribonucleic acid found at the offense scene. DNA engineerings used in forensic scientific discipline probes have improved significantly since the 1980s and still go on to make so due to ongoing research in the field.


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