DNA And Short Tandem Repeats

Nowadays, DNA is a crucial component of a crime scene investigation, used to both to identify perpetrators from crime scenes and to determine a suspect’s guilt or innocence (Butler, 2005). The method of constructing a distinctive “fingerprint” from an individual’s DNA was first described by Alec Jeffreys in 1985. He discovered regions of repetitions of nucleotides inherent in DNA strands that differed from person to person (now known as variable number of tandem repeats, or VNTRs), and developed a technique to adjust the length variation into a definitive identity marker (Butler, 2005). Since then, DNA fingerprinting has been refined to be an indispensible source of evidence, expanded into multiple methods befitting different types of DNA

DNA forensics is a division of forensic science that focuses on the use of genetic material in criminal investigation to answer questions pertaining to legal situations, including criminal and civil cases. Through DNA testing, law enforcement officers are able to identify human remains or the individual responsible for a crime. DNA testing is a highly advanced scientific process that involves replicating the human DNA sequence to create a genetic map of an individual. Because of its reliability, DNA testing has become a significant factor in criminal cases. However, it has also been identified as having the potential to violate privacy and constitutional rights. The DNA identification process consists of five stages. These five stages

RFLP or restriction fragment length polymorphisms became the first scientifically accepted DNA analysis method in the United States (Jones). The repeat segments are cut out of the DNA strand by a restrictive enzyme that acts like scissors and the resulting fragments are sorted out by electrophoresis (Saferstein 391). However, there are some drawbacks using the RFLP method in the forensic science community. The RFLP technique requires a large amount of DNA and must be of high quality and cannot be degraded (Jones). Forensic scientists and the law enforcement community

Beginning in the mid-1980s, the development of DNA analysis technology has revolutionised the field of forensic science within the criminal justice system. As the refinement of procedures and technology continues, even minute samples of biological material (including blood, saliva, semen and skin cells) are able to be analysed and used to link or acquit perpetrators of crimes. (Whitney, R n.d.)

DNA testing is a critical and accurate tool in linking accused and even convicted criminals for crimes, and should be widely used to assess guilt or innocence before jail sentences are imposed. It was started up by scientists Francis C. Crick and James D, Watson in 1953 as they had described the uses, structures and purpose of the DNA “deoxyribonucleic acid” genetic fingerprint that contains organism information about an individual (testing

Today in the crime world, DNA evidence is strongly accepted in solving crime cases. This is all based in part by allowing a crime laboratory to have a designated unit whose main goal is to analyze DNA evidence to aid investigators with positive outcomes in crime case solving. With that being said we are going to discuss the functions of a DNA unit within a crime lab as well as address the vital role these units play in solving crime.

Due to the uniqueness of DNA it has become a powerful tool in criminal investigations

No two people, except identical twins, have identical DNA sequences, which makes DNA testing appealing to law enforcement. Two types of DNA testing include short tandem repeat and variable number tandem repeat. Short tandem repeat requires less DNA compared to variable tandem repeat, which is “useful when a sample has been degraded at the crime scene.” (“DNA Evidence”) Whilst DNA evidence is a useful weapon in solving crimes, it is not infallible; therefore, it needs to be used with caution, especially with partial DNA profile,

DNA forensics can also narrow down suspect pools, exonerate innocent suspects, and link crimes together if the same DNA is found at both scenes. However, without existing suspects, a DNA profile cannot direct an investigation because current knowledge of genotype-phenotype relation is too vague for DNA phenotyping. For example, a profile from a first time offender that has no match in any database may give the information that the criminal is a left handed male of medium stature with red hair and freckles. It would be impossible to interview every man who fits that description. However, with available suspects, DNA forensics has many advantages over other forms of evidence. One is the longevity of DNA. Although it will deteriorate if exposed to sunlight, it can remain intact for centuries under proper conditions (Sachs, 2004). Because DNA is so durable, investigators can reopen old cases to reexamine evidence.

DNA technology has been used as a means to identify perpetrators of rapes and murders with a very high degree of reliability. However, interpretation of the evidence can be problematic at times. This problem comes into play when there are mixed sample’s, partial profiles and with contamination of the evidence submitted. Mixed samples

The DNA Identification Act of 1993 was formerly known as the Omnibus Crime control and Safe Streets Act of 1968. Under the new act forensic laboratories are authorized to analyze DNA for identification purposes that are retrieved from crime scenes. With the regulations of the act the Federal Bureau of Investigation is obligated to follow standards such as setting standards for testing and issuing an advisory board to supervise the standards for quality assurance. Of the results under the act records are established of persons convicted of crimes, samples recovered from crime scenes, and samples from unidentified human remains.

Forensic DNA Phenotyping is a new and emerging field of forensic science. As it is so new, there is very little in terms of literature on this field, very little testing done on this type of identification, and few cases that have used DNA Phenotyping to assist in the investigation. The first documented case of DNA Phenotyping being used is in the early 2000s, so it has had under 20 years of research and experimentation with it. There are many weaknesses to the version of DNA Phenotyping that is available for use so far, but once there is more research done on it, and more experimentation with this new science, DNA Phenotyping could easily be a major tool to investigators around the world.

The results in this lab showed that suspect 2 was a match for the DNA found at the crime scene. This was determined by DNA fingerprinting. In this lab, the samples of DNA from two suspects and the DNA from the crime scene were cut with two different restriction enzymes and then the DNA was run through gel electrophoresis. The different restriction enzymes cut the DNA in different places, so when the DNA was run through the gel, the gel showed two fragments for each sample based on their size. The fragments shown are known as bands of DNA. These bands of DNA for each suspect were analyzed and compared with the bands of the DNA from the crime scene. The bands of DNA were compared based on the distance they traveled through the gel from the wells.

DNA profiling technologies have had a considerable impact on how forensic science and criminal investigation have been understood, carried out, and regulated in the last 25 years. Current methods of forensic DNA profiling (known also as DNA fingerprinting and DNA typing), based on Polymerase Chain Reaction (PCR) amplifications of a varying number of Short Tandem Repeat (STR) loci found at different locations on the human genome, are regularly described as constituting the “gold standard for identification” in contemporary society. Prior to the implementation of PCR based extraction and amplification methods in the 1990’s, the initial uses of DNA fingerprinting (based on Multiple and Single Locus Probes) were largely confined to reactive

Recent advancements in DNA technology have improved law enforcement’s ability to use DNA to solve old cases. Original forensic applications of DNA analysis were developed using a technology called restriction fragment length polymorphism (RFLP). Although very old cases (more than 10 years) may not have had RFLP analysis done, this kind of DNA testing may have been attempted on more recent unsolved cases. However, because RFLP analysis required a relatively large quantity of DNA, testing may not have been successful. Similarly, biological evidence deemed insufficient in size for testing may not have been previously submitted for testing. Also, if a biological sample was degraded by environmental factors such as dirt or mold, RFLP analysis may have been unsuccessful at yielding a result (Turman).