The DNA is one of the latest methods to uncover crimes; thus, most of courts within some countries took the DNA as a proof since 1987. Some of the Arab countries adopted using genetic imprints due to its credibility in inference and proofing.
DNA has a physically powerful ability of proofing than fingerprints as it distinguishes between individuals where there is no probability of DNA similarity between two persons whether they are relatives or non-relatives. DNA is very fine particles in every human cell that determine the characteristics of the person; every cell of the human body carries the same genetic profile. There are no two individuals have the same DNA except twins that split from the same ovum, even though they differ in fingerprints; therefore, DNA can be used to deduce the owner of itâ€¦
Therefore, I'm going to clarify some things about this important field regarding the criminal proofing of some crimes within the following discussion.
Deoxyribonucleic acid - DNA
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DNA is the genetic material that exists inside the living cell to give it its fixed shape and it's the code that determines the function of trillions of cells inside the body. The word "DNA" is an abbreviation of Deoxyribonucleic Acid that forms the basic material of chromosome that exists within the cells of the body to control the genetic traits of living organisms.
The basic feature of DNA is its singularity among individuals with the exception of identical twins. Hence, DNA is essential element to detect criminals especially after discovering new techniques to extract and analyze it to develop criminal database.
According to Watson and Greg; DNA molecule consists of two bands united around each other as a spiral staircase that contains phosphate and sugar sequences. This spiral staircase is made â€‹â€‹up of four combined chemical bases, as; Adenine (A), Thymine (T), Ctiosen (C), and Guanine (G). This partial inside the human body consists of nearly three and half billion bases.
Each set of these bases represent one gene from thousands of genes in the human body. With a simple calculation, we could find that each group consisting of 2200 base that bear a certain gene for a distinctive characteristic, such as; eye color, hair color, intelligence, height, and other features.
Most of the people didn't know the DNA until 1984, when Alec Jeffreys
- geneticist at Lester University in London - published a research which explained that the genetic material may be repeated several times and repeating itself in random incomprehensible sequences; he continued his researches until he found that these sequences is distinctive for a certain individual and can't be similar between two persons with an exception of identical twins. In 1985, he patented the Genetic Imprint and defined it as a way of identifying a person by comparing the parts of his DNA with another DNA samples.
Deoxyribonucleic acid is a longÂ polymerÂ made from repeating units called nucleotides. DNA was first identified and isolated byÂ Friedrich MiescherÂ and the double helix structure of DNA was first discovered byÂ James D. Watson and Francis Crick. The structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pitch of 3.4Â nanometers and a radius of 1.0Â nanometers. According to another study, when measured in a particular solution, the DNA chain measured 2.2 to 2.6Â nanometers, and one nucleotide unit measured 0.33Â nm long. Although each individual repeating unit is very small, DNA polymers can be very large molecules containing millions of nucleotides. For instance, the largest human chromosome, chromosomeÂ number 1, is approximately 220 millionÂ base pairsÂ long.
In living organisms, DNA does not usually exist as a single molecule, but instead as a pair of molecules that are held tightly together. These two long strands entwine like vines, in the shape of aÂ double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a nucleobase, which interacts with the other DNA strand in the helix. A nucleobase linked to a sugar is called aÂ nucleosideÂ and a base linked to a sugar and one or more phosphate groups is called aÂ nucleotide. A polymer comprising multiple linked nucleotides as in DNA is called a polynucleotide.
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The backbone of the DNA strand is made from alternating phosphate and sugar residues. The sugar in DNA isÂ 2-deoxyribose, which is aÂ pentoseÂ (five-carbon) sugar. The sugars are joined together by phosphate groups that formÂ phosphodiester bondsÂ between the third and fifth carbonÂ atomsÂ of adjacent sugar rings. These asymmetricÂ bondsÂ mean a strand of DNA has a direction. In a double helix, the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands areÂ antiparallel. The asymmetric ends of DNA strands are called theÂ 5â€²Â (five prime) andÂ 3â€²Â (three prime) ends, with the 5' end having a terminal phosphate group and the 3' end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugarÂ riboseÂ in RNA.
Primarily two forces stabilize the DNA double helix:Â hydrogen bonds between nucleotides andÂ base-stackingÂ interactions among aromatic nucleobases. In the aqueous environment of the cell, the conjugated bondsÂ of nucleotide bases align perpendicular to the axis of the DNA molecule, minimizing their interaction with thesolvation shellÂ and therefore, theÂ Gibbs free energy. The four bases found in DNA areÂ adenineÂ (A), cytosineÂ (C),Â guanineÂ (G) andÂ thymineÂ (T). These four bases are attached to the sugar/phosphate to form the complete nucleotide.
Methods of getting DNA
Alec was the first person to develop a new technique for collecting DNA; as the following;
Extracting a sample form tissues and fluids of the body, as; hair, blood, sweat.
Slicing the sample by an enzyme - genetic scissors - that can cut the DNA bar longitudinally and separate Adenine and Guanine bases in one side, and Thymine and Cytosine in the other side. http://ars.els-cdn.com/content/image/1-s2.0-S016836590300097X-gr5.jpg
Arranging these sections by electrical discharge to form longitudinal sections from the separated tape and its length depends on the number of repeaters.
Exposing these sections to X-ray film to be printed to appear in the form of parallel and dark lines.
Although the DNA molecules are very small to a high degree (if it were collected from the inhabitants of the whole earth; it won't increase than 36 mg), but the genetic materials is relatively large and clear.
Dr. Alec did not stop his researches regarding this technique as he studied one family to test the inheriting method of such imprint; he found that children are carrying half of their characteristics from the mother and the other half is from the father that differs from one person to another. If the sample was too small than the required it will have another test - Polymerase Enzyme Reaction - to double the amount of DNA in any sample. Researchers showed that DNA does not change from place to place in the human body as it is fixed regardless of the type of tissue; DNA that is in the face is the same DNA from the other body.
Sources of the DNA from the human body
DNA can be taken from multiple sources inside the human body where it can be attained from any cell of the human body. Scientists have identified some positions of the human body to get DNA from them, as; blood, skin, bones, and nails, hair, saliva, mucus, semen, and teeth. There is no doubt that the variety of DNA sources find more space to carry out and develop the criminal research.
In the past, using the hair within the â€‹â€‹criminal investigation was limited to providing personal data about the offender regarding his; age, lineage, and gender. Thanks to DNA, the hair became a strong proof about the crime and against the offender upon using DNA on the basis that the hair shaft contains human cells. The same situation is with the saliva, where it is one of the DNA sources because there are two kinds of human cells in the back wall of the mouth that may attach with the saliva. We can extract saliva from; remains of a cigarette, a postage stamp that pasted with offender's saliva, or from the body of an envelope that was sent, pasted, and closure by the offender. Using DNA, which can't be erased within the criminal sphere, widens the circle of physical evidence.
Places of DNA within the crime scene
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DNA has multiple positions within the crime scene that have DNA sample; where each position may provide a specific source of DNA that might be inside:
Cigarette butts since it catches saliva.
Nail scratches since it catches blood or skin cells.
Edge of the beverage bottles, cups since it catches saliva.
Hats and masks since they catch sweat, skin cells, hair, saliva.
Napkins and towels since it catches skin cells, hair, and saliva.
The victim's underwear before or after the assault since it catches hair, semen, blood, sweat.
Bite marks on the victim's body since it catches saliva.
Rubber condom since it catches semen, skin cells.
Blankets, mattresses or other family covers since it catches semen, sweat, hair, saliva.
DNA advantages in comparison with other evidence
The ability to determine the gender.
Helping the victims to identify some of the missing information about the offender.
Possibility of doubling the amount of DNA in the sample by performing a specific test.
DNA multiple sources which can be drawn from any human cell.
DNA resistance to decomposition and putrefaction factors for long periods.
Uncovering thousands of crimes that charged against unknown where DNA exonerated hundreds of people from different crimes to condemned others.
Readability and computer storability until demand unlike fingerprints.
Protecting the criminal evidences
Evidence of DNA samples play an important role for detecting offenders, so the process of collecting and archiving these samples is very important to prevent any possible corruption or contamination. There are many factors can affect the validity of the evidences like the environmental factors, as; humidity, temperature, sunlight, bacteria, and mold.
DNA evidence can be contaminated when it mixed with another DNA evidence for another case; such contamination may occur in case of coughing inside the crime scene or touching the spot that contain DNA evidence by any member.
Consequently, precision during the collection process of the evidence requires taking strict precautionary measures to maintain the integrity of the collected samples that pending for analyzing and compliance; among these measures are;
Avoid touching the spot that have evidences.
Avoid talking or coughing over the evidence to be collected.
Wearing gloves during the collection process of the evidences and change them constantly.
Put the evidences into new paper envelopes and not in a plastic wallet.