Understanding of Dna, Its Structure and Role

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What is DNA?

DNA, properly named Deoxyribonucleic acid, is within all humans. DNA is a three-part system. The first part is deoxyribose sugar, which is where we get the beginning, deoxyribo. The second part is nucleic. The nucleic is the location of the DNA. Lastly, the third part, is the key component of DNA (Andersen. 2011). DNA is found within the nucleus of all cells that make the foundation of humans and all living beings. In other words, it is the blueprint of everything that is living.

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Nucleotides are the foundation of DNA. Many scientists refer to them as the building blocks of DNA. All nucleotides have three parts. The nitrogenous base is the first part of the nucleotide. This base consists of four chemicals. These chemicals are adenine (A), cytosine (C), guanine (G), and thymine (T). The second part is call deoxyribose sugar, while the third part is the phosphate group (Anderson, 2011).

Each of the chemicals found in the nitrogenous base are paired with each other. Adenine (A) and thymine (T) are paired together, and cytosine (C) and guanine (G) are paired with each other, resulting in base pairs. A nucleotide is made from the base pairs that are connected to phosphate and deoxyribose sugar. Nucleotides are put together in two strands that are connected by hydrogen bonds and as the strands continue to form into what resembles a spiral, it becomes what is called a double helix (Anderson, 2011).

Segments of DNA within a chromosome are called genes. Genes make up certain proteins that help to define how a person looks. Everyone has 23 chromosome pairs, that total to 46 chromosomes. Locus, which helps to determine specific genes such as hair and eye color, is where these chromosomes live. This gene is found within the same locus for everyone. There are an estimated 20,000 genes that hold specific genetic information. This information is within out DNA, known as a genetic code. Every human has a multitude of genetic codes within them that make each and every one of us unique (NSW, 2012). There have been situations when the genetic makeup is faulty, then there is a protein that is not being produced, or it is being produced in the wrong way, which can cause a mutation within a person. This usually occurs when a single base is replaced by another base. This other base is called a base-substitution mutation (Lee, 2014). This usually occurs when a chemical ha been added or deleted from the base. Due to this, all of the amino acids begin to become affected (Lee, 2014). Many types of mutation can occur due to growth defects, the body development, and the way that the body works as a whole.

Using DNA for Profiling

As stated above, DNA is the blueprint for all human beings. Approximately 99.9 percent of our DNA is similar (How DNA Profiling works, 2011). In order to find out the remaining .01 percent in a DNA sample, a forensic scientist may use a DNA profiling test from miniature amounts of DNA that had previously been collected from either a victim or a crime scene. Step 1 in this process is the Polymerase Chain Reaction (PCR). This method is used to analyze and to duplicate small samples of DNA. The PCR method has the ability to analyze the most minute sample of DNA. There are three steps to the PCR method; denaturation, annealing, and extension. All of these steps use different temperatures that range from 54 degrees Celsius to 94 degrees Celsius. This cycle is usually repeated for 30 to 40 times. Throughout each cycle, a DNA double helix is broken, duplicated and then put back together in order to raise the amount of DNA. Amplifying DNA is very critical to cases, because there usually is not much DNA available to process. If a small amount is processed without the use of amplification, then the DNA can lose its integrity and ultimately become compromised.

Another method used for DNA profiling is Short Tandem Repeats (STR). STR extracts DNA from specific areas within the nuclear DNA. The section of DNA that has been extracted is then amplified using the PCR method. Using the STR is a very beneficial method to use because four to five nucleotides are repeated and the information that comes from being analyzed is more accurate and precise (, n.d.). When used in a criminal case, in order to consider it a perfect match, 13 STR loci must be able to match the person who is being accused.

How CODIS is used within a Criminal Case

The Combined Index System (CODIS), is a system database that store all of the DNA that has been collected from a victim or at the scene of a crime. CODIS was invented by the Federal Bureau of Investigations (FBI) as a tool to assist in housing and comparing all DNA that is sent from forensic labs at local (LDIS), state (SDIS), and national (NDIS) levels (FBI, n.d.). This database is able to examine and compare any new DNA to DNA that has been previously stored within the system. The previously stored DNA can be a tool used to possibly link DNA from a crime scene that does not have a match, link cases together, or cases that have gone cold. All states within the U.S. has the ability to serve as their own SDIS. CODIS has different levels and every level has their own protocols for storing DNA. Of all the levels, LDIS is not as strict with their requirements as NDIS (FBI, n.d.). When DNA has not been matched to a person, it is still entered into CODIS and stored until a match is found. Once a match is made, it is then removed from CODIS.

Being Exonerated through the use of DNA Testing

Marvin Anderson was the 99th person to ever be exonerated (The Innocence Project, n.d.). Mr. Anderson was falsely charged and convicted of 2 counts of rape, abductions, robbery, and forcible sodomy of a Caucasian woman back in 1982. The victim reported that she was held at gunpoint and raped by an African-American male who was riding a bicycle. At the time that the crime was reported, the officer whom took the victim’s statement, considered Anderson to be his top suspect because during the crime, the offender stated that he “had a white girl.” Because of this statement, the officer could only recall one African-American that he knew that was in a relationship with a Caucasian woman during this time (Innocence Project, n.d.). In order to convict Anderson, the officer acquired photos that were in black and white to use in a photo line-up, yet had a single colored photo of Anderson for the victim to identify her assailant, and she did identify him as the offender.

At the start of Anderson’s trial, many people within the community felt that John Otis Lincoln was the one responsible for this woman’s assault, and not Mr. Anderson. There were many things that proved that Mr. Anderson had no involvement, such as, he had an alibi for the time of the crime, he was with his Caucasian girlfriend at the time of the crime, the true owner of the stolen bike reported that it was stolen from him by Lincoln just hours before the rape happened. It was Anderson’s legal counsel who denied having Lincoln on the stand as a witness, nor was it allowed for the owner of the bike to testify (The Innocence Project, n.d.). Anderson was convicted by a jury, that was not of his peers of this crime and was sentenced to 210 years in prison. When Anderson was fighting this case, the use of DNA testing had not yet been made available. His entire stay in prison, Anderson professed that he was innocent of this crime. After DNA testing had become available, Anderson requested to have the semen sample from the rape kit to be tested. In 2001, his request was finally approved, however, by this time the DNA had degraded and it only had four STR markers remaining (The Innocence Project, n.d.). Anderson served 15 years in prison, but on August 21, 2002, he was finally exonerated due to his DNA clearing him as the offender.

In 1983, Kirk Bloodsworth was convicted of first degree murder, sexual assault, and rape of a 9-year-old girl from Maryland. Five witnesses placed Bloodsworth at the scene of the crime, claiming that he was with the victim. During sentencing, Bloodsworth received two life sentences that were to be served consecutively (The Innocence Project, n.d.). During his stay in prison, Bloodsworth found out about DNA profiling. It was because of his attorney’s persuasion that officials allowed the DNA of Bloodworth to be tested against the DNA that was found at the scene of the crime. The Forensic Science Associates (FSA) performed the DNA test in 1992, that was agreed upon by the prosecution. PCR was the chosen method that ultimately compared the victim’s blood stain and Bloodworth’s DNA to the DNA that was found on the victim’s underwear, her shorts, a slide that was gained during her autopsy, and a stick that was found at the scene. While comparing the spermatozoa, it was concluded that there were not enough spermatozoa to compare, however, Bloodsworth DNA did not match the DNA that was found inside of the victim’s underwear. After spending eight years on death row, Bloodsworth was finally released from prison, in June of 1993.

Frank Lee Smith was not as lucky as the two previously mentioned men who were falsely imprisoned. He died before he was able to be exonerated. Frank Lee Smith was from Florida, where he was falsely identified and then convicted of the rape and murder of an 8-year-old girl named Shandra Whitehead (PBS, n.d.). Whitehead was murdered on April 15, 1985 due to blunt force trauma to her head. At her autopsy, it was found that she has been sodomized and raped. The night of Whitehead’s death, her 19-year-old neighbors, Gerald Davis and Chiquita Love stated in their report that the offender was an African American man who stood at 6 feet tall, and had a full beard, his hair was “scraggly,” and he had droopy eyes. A sketch was drawn up, and it was the composite sketch that led the police in the direction of Smith, which ultimately led to his arrest on April 29 (The Innocence Project, n.d.). Unfortunately for him, it was his prior criminal record that helped the prosecutors to turn the case against him. With his prior record and the mother of the victim testifying that she had witnessed Smith leaving the scene of the crime from her living room window, it was easy for the jury to reach a unanimous decision of a guilty verdict. In 1986, Smith was convicted and sentenced to the death penalty (The Innocence Project, n.d.). After spending 14 years on death row, his DNA was finally able to be tested against a semen sample that had been collected during the autopsy of little Whitehead. In January of 2000, Smith passed away from cancer, and just 11 months later, on Dec 15, 2000, he was finally exonerated (PBS, n.d.).


The use of DNA has made tremendous leaps and bounds throughout the years. It has been shown that the use of DNA within criminal cases has been shown to be extremely useful. Not only does DNA benefit the defense, but it also beneficial to the prosecutors. It has been approximately over 350 people who have had the use of DNA in assisting them with their exoneration within the Unites States (The Innocence Project, n.d.). Over 205 of those exonerated have been African American, over 95 of them have been Caucasian, approximately 22 have been Latino, and about 2 have been Asian American (The Innocence Project, n.d.). Using DNA for solving crimes will continue to be a widely used method. This method will continue to progress and advance within the future. With CODIS being so efficient and effective at storing DNA, it will continue to be used to assist in either simplifying the convictions of those who are guilty, or assisting in exonerating those who are innocent.

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