A criminal investigation has become more advanced with the introduction of DNA profiling systems. With the increasing sophistication of criminals, it would be quite impossible to convict criminals in the absence of forensic science. Thus with the use of evidence that would have been invisible to the naked eye, it makes forensic science one of the vital tools in conducting criminal investigations. The structure and composition of DNA are some of the factors that greatly contribute to the use of DNA in forensic criminal investigations. The following is an introduction of the DNA structure followed by an explanation of how the components have been used to come up with different DNA profiling systems that are utilized in a criminal investigation.
Several DNA profiling techniques exist and most of them can be considered equally effective. This is because in most cases the technique that is to be used will highly depend on the kind of DNA materials that have been retrieved from the crime scene. DNA profiling systems include; “single nucleotide polymorphism (SNP)” profiling, “mitochondrial DNA” (mtDNA) analysis, “human leukocyte antigen” HLA profiling, gender profiling, Y-chromosome profiling, and polymerase chain reaction (PRC).
Deoxyribonucleic acid (DNA) is a genetic chemical code that specifies the appearance of an individual in unique ways. The formation of DNA is usually through the combination of DNA from the parents in a ratio of 1:1; therefore DNA is usually used in testing the paternity of a child. DNA is found in almost all cells of the body including perspiration, semen, all body fluids, hair roots, and body tissues. Chromosomes have DNA as the main constituent.
Almost every human cell contains DNA which in most cases is found in two compartments referred to as organelles. The nucleus and the mitochondrion are the organelles. There are two types of DNA the nuclear also referred to as the genomic DNA, and the mitochondrial DNA (mtDNA). Genomic DNA is what is usually referred to as in most instances; This DNA constitutes 99.7% of all DNA contents. The genomic DNA is arranged in tiny structures known as chromosomes which contain DNA and proteins. Body cells except sex cells are somatic. All somatic cells have 23 chromosome pairs. Sex cells have a single set of chromosomes.
Mitochondrial DNA, which is from the mother’s side is usually used to determine ancestral lines and verify the identity of human remains, can be obtained from bone samples and hair roots. mtDNA is found in the mitochondrion which is cellular organelles; the mitochondrion provides energy for all processes in the cell including cell division and chromosome replication. The mitochondrion is self-reproducing organelles that are semi-autonomous in nature and they are about 200-400 mitochondria per cell (Semikhodskii pg 4). In some cases evidence may not be suitable in the development of DNA profiles using RFLP or STR analysis. This is mainly because while RFLP and PCR techniques utilize DNA obtained from the nucleus of a cell, mtDNA technique uses DNA found in the mitochondrion thus hair shaft and bones cannot be suitable for STR and RFLP techniques so mtDNA analysis becomes more appropriate.
All sperm and egg cell have unique properties with regards to DNA and should they be analyzed individually one would get varying results from cell to cell, however when analyzed millions at a time, the resulting DNA profile will be similar to the ones obtained from somatic cells since individual differences of the sperm cells cancel out. DNA remains unchanged at all times except in cases of mutations. The mutation affects the cells and thus complicates analysis of the results (Semikhodskii pg 5).
In the Y-chromosome analysis genetic markers have been found in the Y-chromosome that can be used in forensic science, in most cases it is used to determine family relations between males as it is passed directly from a father to all his sons. Y-chromosome analysis simplifies the process of extraction and separation of semen and virginal cells prior to analysis in rape cases. In most cases in DNA profiling, the first approach is usually variable number tandem repeats (VNTRs) which are repeated units of a DNA sequence.
The DNA molecule structure is composed of a double helix structure of vertical pieces comprised of alternating sugar molecules and phosphate groups. Each strand contains nucleoside base pairs. The sequence of these nucleoside base pairs is particular to an individual. DNA is composed of genes, which make up a small part of the molecule. Most of the remaining part of DNA has no known function and is usually known as spacer DNA. DNA is composed of a sequence repeated end on end several times. DNA profiling utilizes positions in the human genome that do not code with protein. These positions contain repetitive DNA sequences. Small repeated sequences are known as microsatellites, the number of times a sequence is repeated is determined by the type of profiling known as short tandem repeats (STRs). DNA has certain properties that make it suitable for criminal investigations and revelation of relationships between individuals and the ways in which they are related; the DNA of an individual remains unchanged irrespective of age, the most crucial property of DNA is that it has a unique genetic code unique to every individual. Our DNA dictates the color of our eyes, hair color and height. “DNA is present in every one of the trillions of nucleated cells in the human body” (Becker pg 139). DNA fingerprinting is unique to an individual and two identical fingerprints are yet to be found, the identifiable properties of a fingerprint are known as ridge characteristics (Becker pg 122). An individual’s fingerprint will enlarge with growth but ridge characteristics however remain unchanged.
In processing forensic DNA samples, DNA is extracted from a biological material obtained from the crime scene, the DNA is then measured to establish the amount of DNA recovered. After that specific regions of the DNA are focused on and copied with the polymerase chain reaction (PCR). “Commercial kits are mostly used to enable Simultaneous PCR of 13 short tandem repeat markers” (Butler pg 1)
DNA testing immediately replaced fingerprinting as a tool in a criminal investigation after its introduction with heavy reliance on forensic DNA testing globally. With the development and reliance on DNA testing technology there was the establishment of DNA databases in several countries, reasons that strongly favored DNA testing as opposed to other methods in forensic science include; DNA has high discriminative properties in terms of similarity between two DNA profiles, DNA obtained from the same individual but different sources have similar patterns. The semen of an individual in a particular crime scene will yield the same results as a blood droplet in another crime scene provided that they were from the same person. The DNA can be retrieved from old archives since it is reliable and does not age; it also displays a stronger characteristic when subjected to harsh conditions, unlike protein which cannot withstand both natural and manmade injury. High molecular integrity associated with DNA enables the analysis of samples that have been exposed to extreme temperatures and chemical treatment. The possibility of extracting multiple identical copies of DNA through enzymatic reactions enables genetic information from extremely tiny amounts of biological samples to be obtained. Today’s technology is so advanced that a single hair or droplet of perspiration in a crime scene can be used to obtain the DNA profile of the owner , information in the DNA can be used to determine the gender of the individual (Semikhodskii pg 1). Thus this can have an impact on the direction that criminal investigations will take. A case in point is the indication from DNA samples that the criminal was a female, while the potential suspects in custody are all males, which will call for the criminal investigator to repeat the DNA analysis, or re-evaluate the suspects.
There are concerns that DNA profiling results can be used to invade a person’s privacy. This is mainly from the perspective that there is a possibility that the information can land in the wrong hands who may present a potential threat to the owner. DNA databanks contain DNA profiling information that does not provide any details about the individual’s health status or being a carrier of a disease because non-protein-coding of DNA is approved. Thus unless the DNA profiling is conducted in an unethical manner, the DNA profiling procedure in criminal investigations cannot be considered an invasion of privacy when viewed from this perspective. DNA testing is highly specific and there are few chances the test is giving false information. DNA profiling is the genetic analysis that determines DNA patterns. DNA profiling is a technique used by scientists to assist in the identification of a person by their respective profiles.
DNA analysis was in the first time used in 1986 in solving the Enderby murder case. In the murder case, two murders 1983 (Lynda Mann) and 1986 (Dawn Ashworth) were committed in the same manner. This prompted specialists to analyze forensic samples since seminal fluid from both murders indicated that it was committed by the same person. Richard Buckland confessed to the murder of Dawn Ashworth but denied the murder of Lynda Mann Evidence indicated that the perpetrator was the same individual but did not match that of Richard Buckland. Later on Richard Buckland was convicted with Ian Kelly for these murders. PCR-based testing was developed in less than five years. In solving this case Jeffreys used multiple-locus VNTR genotyping which was soon adopted by forensic science services (Semikhodskii pg 22).
DNA fingerprinting was developed in 1985 by a genetic specialist called Alec Jeffreys. DNA profiling is a new field that witnesses new developments constantly, modern-day DNA profiling normally referred to as STR analysis is a sensitive technique that works on limited sample material even a few skin cells. Among the most recent developments in DNA profiling is the introduction of a portable device that uses DNA left in a crime scene to identify the suspects within an hour after the crime was committed (Gray pg 1).
In India where the prospects presented by DNA profiling are largely unexploited, every year, estimates of thirty-five to forty thousand bodies are disposed of unidentified due to poor DNA profiling. Out of this figure, an approximated 1,500 per year are found dead lying in the streets of the capital city (The Times of India, pg 1). With a conviction rate of 5.8% in 740 cases of sexual harassment, only 35 offenders were convicted. It takes a trial about seven years to close in each of the cases. The case of India pronounces clearly the importance of DNA profiling.
There exist several DNA profiling systems with the most common ones being short tandem repeat (STR) profiling and restriction fragment length polymorphism (RFLP) profiling.
Restriction fragment length polymorphism (RFLP) the DNA is split into small pieces by an enzyme. This sequence-specific enzyme splits the DNA whenever there is a specific sequence of bases. The process by which these fragments are separated is referred to as electrophoresis, after which a sample is placed on the end of a bath containing jelly-like substance known as agarose gel at which point voltage can be applied. The voltage applied makes the fragments that are charged migrate to the opposite end of the bath of gel. Since separation is based on relative molecular weight, large fragments will move slower than small fragments. After electrophoresis both the gel and the fragments are exposed to 0.25M HCL to enable fragment transfer this is followed by washing with sodium hydroxide. The DNA is transferred to a nylon membrane for examination. The minisatellite part of the DNA is examined by radiolabeled pieces of single-stranded DNA known as probes. A probe pairs with its complementary sequence on the membrane. The radiolabeled membrane produces an autoradiograph when exposed to a film. Different fragments are studied. The distribution of the probed regions of the DNA in the population is approximated from the population database to give an estimate of the chance that the sample was from a given suspect.
The short tandem repeat profiling (STRS) is a recent generation of DNA profiling that involves examining microsatellite repeated regions this process involves a cycle of reactions where DNA is split, replication after splitting and then replication again. The number of copies of the initial template has an exponential increase due to this repeated replication. The reaction, which is under kinetic control, reaches a plateau that is dependent on competition, inactivation of the enzyme which acts as a catalyst and the initial number of template molecules. The DNA is split at a temperature of 94 degrees Celsius after which short strands of DNA referred to as primers are attached to the target DNA at particular sites. Bases are added to the end of the primers leading to the formation of complementary strands. The process is repeated to reproduce many copies of the initial template. Because the original material is increased, this technique becomes useful in the analysis of small amounts of DNA. The increase is separated by the process of electrophoresis through an ultra-thin denaturing gel known as polyacrylamide gel. This technique is usually performed manually with replicates observed using silver staining the manual method utilizes three loci including another male/female sex test, although it can also be performed automatically with multiple loci observed simultaneously through fluorescent dyes. The automated method examines four loci. Statistical analysis is carried out on the availability of the observed patterns in the population. STR evaluates particular regions (loci) of the nuclear DNA. The probability that any two individuals, with the exception of identical twins, will have the same 13-loci DNA profile can be as low as 1 in a billion. The FBI has 13 specific STR loci to be used as the standard CODIS. The main reason for establishing a set of loci is to make sure that most forensic laboratories can establish uniform DNA databases with the possibility of sharing forensic information.
Since the introduction of DNA typing in the mid of 1980s it has revolutionized forensic science in the ability of law enforcers to match suspects to crime scenes. Thousands of cases every year around the world have seen guilty suspects convicted and others acquitted because of a biological witness left at the crime scene (Butler, pg 1).
Combined DNA index system (CODIS) when used with new analysis technique supports the argument through searching for possible potential DNA evidence to reevaluate unsolved crimes. CODIS is a computer-based network connecting forensic DNA laboratories at all levels (national, local and state levels). CODIS software allows the comparison of DNA profiles electronically, simplifying the process of linking serial crimes with certain suspects. This is made possible by matching DNA profiles obtained from crime scenes with profiles in the CODIS system. When a DNA profile is created from evidence obtained in a crime scene it is fed into the forensic index of CODIS the software searches through DNA profiles of convicted individuals.
CODIS also aids in the investigation of missing persons by searching the missing person index, which is comprised of unidentified person index and reference index.
The CODIS is designed in such a way that it consists of hierarchical levels, these levels are: Local DNA Index System it is usually operated by police departments and can be transmitted to the state and national levels. The state DNA index system (SDIS) is such that every state has its laboratory that allows local laboratories within the state to compare profiles. The SDIS also acts as a link between the local and national levels. The national DNA index system is the highest level of the CODIS is used by state laboratories to compare profiles. The NDIS is controlled by the FBI.
There are several factors that limit the use of DNA profiling techniques. The main factor that restricts the use of DNA testing when conducting criminal investigations is the kind of investment, in resources, that the DNA profiling technique demands. Most criminal investigators in undeveloped and developing countries also lack educated personnel that can act as forensic scientists.
DNA profiling has its shortcomings, for example in STR, if very small quantities of DNA are retrieved from a crime scene and it is degraded, either not all regions will amplify in the genome, or there is a possibility of discriminatory amplification of DNA in only one of chromosomal STR region. This usually affects the results and leads to forensic scientists drawing false conclusions.
In the united kingdom from the year 1995, under the criminal justice and public order act, DNA samples of all people arrested have been linked with their personal information and genetic profiles are stored in computer database, while the DNA sample is stored in the laboratories this information is kept whether an individual is convicted or acquitted. This to some individuals is considered a serious invasion of privacy since the data is collected without consent and kept permanently. Britain’s National Black Police Association expresses concern 37% of black men and only 10% of white men in the United Kingdom are in the current DNA database, raising concern on racial bias since it seems to be a determining factor in inclusion in the database. Technological advancements allow DNA to be used in familial screening, if DNA from a crime scene does not match any in the database, but there is a match sufficiently close enough to suggest a biological relationship between DNA on the database and the perpetrator. Similar DNA profiles are shared by members of a family and by being related to a suspect in a crime scene, one may be subjected to unnecessary suspicion.
In the RFLP profiling technique, regions in RFLP are large; it is difficult in most cases to separate the fragment using electrophoresis. The smaller fragments will move faster than the bigger fragments therefore it creates a problem when the movement of two VNTR is identical, even though they may differ in length. This is largely due to limited resolution of the gel matrix (only big differences may be detected). Thus a large amount of purified, high-quality DNA is required for this technique to yield uncompromised results. This technique demands high purity in terms of extraction and handling because for example in the case of a sample that is blood extracted from cloth, the dye in the cloth may change the mobility of the extracted DNA in the gel, making analysis quite complex. In this case forensic scientists have to devise a standardized approach that contains all the positive and negative aspects of DNA typing that are to be used as evidence in court (Enotes para 17).
Apart from the shortcomings of the profiling techniques another major challenge that faces DNA profiling is the possibility that there were errors in sample extraction, handling or even in the analysis precautions are usually taken to minimize these errors but they cannot be entirely eliminated, a case in point is the O.J. Simpson case where effects of mishandling blood evidence jeopardized the evidence of the trial, an experienced forensic technician handled DNA evidence with bare hands. The defense was fast in raising issues of violation of scientific procedures and possible contamination of blood evidence. The possible impact of improper investigative conduct was majorly deliberated by the jury. The innocence project utilizes DNA analysis to free prisoners wrongfully convicted and what is surprising is that two-thirds of about two hundred convicts the project has helped to free were convicted based partly on faulty scientific evidence (Connoll, Keller and White pg 452).
Samples taken without consent and reason do not respect privacy and since DNA contains vital genetic information, it becomes more sensitive than any other personal information, such information, if it falls on the wrong hands, can be damaging to an individual’s self-esteem or even career, for instance someone with access to DNA database may use it to deny someone a job because the DNA of that individual indicates a relationship with that of a criminal (Connolly, Keller and White pg 452).
Freedom is at risk with the use of the database, for example a British subject was arrested based on a comparison of six match points of his DNA with DNA found at the scene of robbery which identified him as the thief. His alibi proved he could not have been the perpetrator of the crime which prompted Britain to admit that six-match points were not enough to conclude accurately, and the points would lead to reduced accuracy as more samples were added to the data bank. The United Kingdom agreed to share its DNA database with other European countries, an action that further compromises the privacy of whoever has their DNA stored (Scottish Police Services Authority para 4), DNA portrays the highly sensitive details of a person which may include susceptibility to emotional and physical disorders (Connolly, Keller and White pg 453).
Even though DNA testing has been used to free inmates wrongly convicted, as well as convict others, certain courts have favored certain methods while directing the court trials to examine other testing methods more carefully. The modes of collecting and analyzing evidence through DNA typing has also been challenged by many defense attorneys (Reid pg 146)
Sample contamination is definitely inevitable in the investigation since in most cases most crime scenes do not meet the hygiene standards of medical laboratories. Analysts are of the belief that anything that is not at par with absolute purity in body samples lowers the reliability of the DNA profiling process. An expert in DNA analysis, when called into a crime scene, shoulders the responsibility of stating the nature of the sample extraction in terms of contamination and possibilities of reducing the contaminants without affecting the purity of the sample. The expert also has to indicate how the sample was contaminated, if the contaminants were removed before profiling and the mode of removal of the contaminants (Becker pg 139-140).
Forensic laboratories must ensure that high levels of quality control are maintained. However when properly handled biological evidence can provide reliable DNA profile that can last for years after analysis is done. Developments in DNA analysis techniques enable forensic laboratories to establish profiles from biological evidence that is not visible to the naked eye in most cases skin cells. DNA analysis usually requires a comparison between two samples; the “question sample” Q and the “known sample” the K, in forensic cases Q represents the crime scene evidence, while K is the suspect’s sample.
Biological evidence retrieved from a crime scene has the ability to exclude or associate an individual from participation in a crime, more specifically direct transfer of DNA from an individual to an object in a crime scene links that individual to the crime scene. In crime scenes proper evidence collection in terms of DNA, even though emphasized, can never be deemed perfect because initial contamination of DNA sample jeopardizes the information obtained and may lead to ambiguous results. It is strongly recommended that clean latex gloves be worn for each item of evidence. Items should be packaged separately to limit contamination. To prevent degradation of DNA molecules, paper envelopes are more appropriate than plastic bags since water condenses in plastic bags during high humidity. Bloodstains and semen are air-dried before packaging to prevent molds from growing in them (Butler pg 7).
DNA profiling is a welcome idea if it targets providing watertight evidence in cases where traces of evidence are left at the crime scene. Nevertheless, DNA profiling creates a lot of ethical issues more so the likely discrimination that comes with it. Moreover, it is possible to implicate persons wrongly if databases are searched for DNA profiles that are close to those of suspects. DNA profiling, therefore, needs to be embraced with a lot of caution. Researchers in this field ought to do more to remove the few setbacks in DNA profiling; this will increase its acceptance among citizens.
Bagai, Eric. What is the importance of DNA forensics? n.d. Web. 2011.
Becker, Ronald F. Criminal investigation. Burlington, MA: Jones & Barlett Learning, 2010.
Biotechnology Online. DNA profiling. 2011. Web.
Butler, John M. Advanced topics in forensic DNA typing: Methodology. Waltham, MA: Academic Press, 2011
Connolly, Peggy et al. Ethics in action: a case based approach. Malden, MA: Wiley- Blackwell, 2009. Print.
Enotes. DNA profiling. n.d. Web. 2011
Gill, Peter, Ivanov Pavel L, Kimpton Colin, Piercy Romelle, Benson Nicola, Tully Gillian, Evett Ian and Hagelberg Erika. “Identification of the remains of the Romanov family by DNA analysis.” Nature Genetics 6; (1994):130-135. Print.
Reid, Titus S. Criminal justice essentials. Hoboken, NJ. John Wiley & Sons, 2011. Print.
Scottish Police Services Authority. DNA. n.d. Web. 2011.
Semikhodskii, Andrei. Dealing with DNA evidence: a legal guide. New York, NY: Routledge, 2007. Print.
The Times of India. “Can DNA profiling help in identifying unclaimed bodies?” The Times of India, 2009. Web.