DNA (deoxyribonucleic acid) testing is a scientific method used to distinguish among living entities through the variations between strands of DNA. It is hard to believe that the use of DNA testing first entered the forensic world just 25 years ago. From the criminal cases shown by the media to the new popular television series CSI, the importance of DNA analysis is well-known.
The advancement in science and technology has allowed the development of DNA testing techniques, allowing scientists to solve questions once deemed unsolvable. Not only are we able to determine who the rightful father is in a parental dispute or the guilty party in a criminal investigation, but technology now has the ability to uncover the identity of thousands of body fragments from the September 11, 2001, terrorist attack on the World Trade Center, in New York City.
Furthermore, the use of DNA testing has played a significant role in tracing back human ancestry. By following mitochondrial DNA back through time, one is able to track the migration of specific genes through maternal lineages. DNA testing has greatly enhanced human curiosity and our understanding of the world in which we live.
Genetics and Molecular Biology
DNA is the foundation of life. Within each living cell, there is a nucleus that holds thousands of paired genes within structures called chromosomes. In human beings (who are considered normal), there are 46 chromosomes composed of strands of DNA, which include 22 pairs of non-sex-determining chromosomes (autosomes), along with one pair of sex-determining-chromosomes; an X chromosome from the mother and an X or Y from the father. The sex chromosomes determine whether the child will be male (XY) or female (XX). Except for sperm and egg cells and cells that do not have a nucleus, such as blood cells, the genetic makeup of our entire body is in every cell.
The double-helix “rope ladder” structure of DNA was discovered by James Watson and Francis Crick in 1953. They found that within each chromosome are strands of DNA, which are composed of long chains of base pairs: guanine (G), adenine (A), thiamine (T), and cytosine (C). The chemical properties allow Base A on one strand to pair with T on the other, and G to pair with C. Thus, depending upon the specific order and pairings, a gene that consists of various lengths of base pairs encodes for specific proteins. This instructional ability does not include every length of DNA, for the majority of DNA has no known function. The locus is the molecular location of a gene along a strand of DNA, and every chromosome contains a specific order of loci, which is the same in all humans. For example, on Chromosome 7 in every human, there is a gene that, if altered, may cause cystic fibrosis.
The Advancement in Testing Techniques
The first method of DNA testing used by forensic labs was restriction fragment length polymorphism (RFLP). Although it was first discovered in 1980 by David Botstein and coworkers, it was Sir Alec Jeffreys (English biochemist) who first discovered its application in “DNA fingerprinting.” Jeffreys brought DNA fingerprinting into the criminal justice system to identify criminals and/or determine innocence of those wrongfully convicted. This technique is based on distinguishing variation in the length of DNA at particular loci (location on the chromosome). Thus, it is able to determine whether two different samples are from the same source. Although RFLP has the ability to discriminate a large number of loci, it has a number of drawbacks. It requires a large amount of DNA and has difficulty using degraded or old samples, which are quite common in forensics. In addition, it is a long and difficult task to perform; therefore, it will eventually be a technique of the past. Other early techniques included the human leukocyte antigen analysis (HLA DQAI), which examined only one locus; the AmpliType PM+DQA1 system; and amplification fragment length polymorphisms (AMFLPs).
With advancement in technology, new techniques were developed that were less strenuous, faster, and had the ability to target mitochondrial DNA, X and Y chromosome markers, and short tandem repeats. A variable-number tandem repeat (VNTR) is a region of DNA that differs in the number of consecutive DNA sequences that are repeated throughout a chromosome. The first of the two main techniques, VNTR typing, utilizes the extensive variation of VNTRs among individuals along with regions of identifiable length to help differentiate humans. In 1983, Dr. Kary Mullis developed the polymerase chain reaction (PCR), in which large amounts of DNA can be replicated from a small sample of DNA (from a strand of hair or on a stamp). Once the DNA is amplified, the process continues similar to that of VNTR. The PCR method has a few drawbacks that can reduce its efficiency. Initially, if the genes are contaminated, then the process will amplify the wrong DNA. And second, because some of the loci used in PCR are functional genes, there is a higher probability that they would be influenced by natural selection, thus changing the frequencies of various genes throughout the human genome.
Typically, the DNA is amplified and then analyzed for specific characteristics. With the advances in technology and the Human Genome Project, a third method known as “DNA sequencing” or the “Sanger method” was developed. This technique is able to unravel specific DNA sequences base by base, to be used for making detailed comparisons to determine similarities and differences between strands.
Uses, Accuracy, and Limitations
The most common purpose for DNA testing is in criminal cases to identify and confirm a suspect’s innocence or guilt. This is extremely important, because some cases would not be solved without DNA evidence. With enhanced techniques and decreased costs, testing is now used not only for murder and rape cases, but for everyday disputes, including pet ownership, burglaries, marital infidelities, and so forth. Parental testing for identifying the rightful father of a child is a common use in custody cases. In addition, preserving children’s DNA in commercial kits will assist in helping to identify lost children who are found. Many more uses include following genetic disease incidence, prenatal testing, genetic mapping, the Human Genome Project, identifying human remains (soldiers, victims of the World Trade Center), among others. The use of DNA testing has proven crucial to many aspects of society today.
The world of forensics has assisted in the rapid improvement in DNA-testing techniques that are available today. In only a few decades, technology has advanced in such a way that DNA analysis has gone from taking months to conduct to being able to perform within a few hours. The technical aspect of DNA analysis has consistently proven itself; however, there are a few limitations. The primary weakness has been found through human error within procedure and lab methods. For example, there is error when testing two samples that are shown to originate from the same source when they actually are not from the same source. DNA testing may produce false positive or negative results. False positive results occur when testing results show a suspect sample is that of the forensic sample when it is not. False negative results are when testing results show suspect DNA is not the same as forensic sample when it actually is. However, there is no exact error rate, because error cannot be predicted, nor will it remain constant. The statistics show that in a trial, the source of the DNA is 1 million times more likely to be the suspect’s than another random person’s with the same genetic profile.
The FBI has strict standards and regulations on DNA testing and validity for “accuracy, precision, and reproducibility.” These regulations include documents that characterize the loci of genes on a subject’s DNA and the distribution of genes within the population from which to compare. Furthermore, evidence samples must be collected in an appropriate manner and handled according to procedure, while labs are to use reputable methods and techniques to analyze and interpret DNA samples. The FBI uses statistics to determine if DNA information is valid and unique to the suspect. Consequently, if the profile frequency of the suspect compared to the entire U.S. population is less than 3.9 x 10(-11), it is 99% certain the DNA in question did not come from another individual.
In tragedies such as the World Trade Center attack, victims’ bones and body parts are compared with DNA from their toothbrushes, hairbrushes, razors, and so forth, to allow DNA sequence comparison in order to be able to give remains to relatives. Also, DNA (along with proteins and lipids) from ancient organisms is able to be accessed through fossils, soil, and rocks to help bring greater understanding of biological history. This brings together the disciplines of archaeology, paleontology, molecular biology, geology, and chemistry.
If enough DNA from an ancient organism is discovered and the damage to the DNA was not severe, the possibility of cloning would still exist. The cloning process takes certain portions of DNA from one species and inserts it into that of a host organism that is similar to the organism in question. Utilizing the host’s natural ability to grow and reproduce, the organism could modify the donor DNA with the ancient DNA, creating a larger segment of DNA, and the organism can gradually “rebuild” the ancient organism. This can provide evidence to show relations of organisms to one another and help to rebuild species ancestry, a “phylogenetic tree.”
Scientists also use DNA analysis to look at tissue remains on skeletons from mummified bodies. Since mummies underwent rapid drying, it was thought that rehydration of tissues could allow visualization of nuclei and subsequently genetic material could be extracted. For example, in 1981, nucleic acids from a preserved liver from a 2,000-year-old Han Dynasty corpse were isolated by G. Wang and C. Lu.
The mitochondrial (mt) DNA studies have had a significant impact on tracing human ancestry. These studies are based on the assumption that mtDNA is solely inherited from the mother and does not undergo genetic recombination. For example, the mtDNA analyses of the “Iceman” found in the Tyrolean Alps of Italy determined that he was an ancestor of current Europeans living north of the Alps. If the assumptions are true, then mtDNA studies will continue to increase our knowledge of maternal lineages and human evolution.
The most common use of DNA technology involves the collection of blood, semen, skin, and hair samples at crime scenes that are used to extract DNA and identify the donor. The DNA is first isolated, and amazingly, even if there is a trace amount of blood present at the scene, DNA can still be extracted and suspended in a liquid with the proper use of chemicals and heat. Once analyzed, DNA is stored in databases so that in the future, DNA profiles can be searched.
After being convicted based on circumstantial evidence and/or eyewitness testimony, many criminals have been sent to prison or put to death. Within the legal system, there have been many cases in which the guilty have been set free and the innocent have been put behind bars or even placed on death row. Since 2002, there have been 102 cases in which men were wrongly convicted and freed from death row because of DNA technology.
Ronald Jones spent 10 years on death row after he was convicted of a 1989 rape and murder of a woman from Chicago. Jones was one of the first to be proven innocent by DNA testing. The trial almost did not occur because Judge John Morrissey dismissed Jones’s request; however, the Illinois Supreme Court ordered DNA testing to take place, which proved his innocence. Another example is Robert Earl Hayes of Broward County, Florida, who was convicted of rape and murder and put on death row in 1991. The difference in this case is that it was due to faulty DNA technique that lacked proper validity. After Hayes had been on death row for 4 years, his DNA was retested using more acceptable methods of analysis. Hayes was finally acquitted in 1997. Furthermore, in 1987, in a rape case in which semen was tested from a victim’s vagina, Tommie Lee Andrews became the first American to be convicted due to DNA evidence.
Since the discovery of forensic DNA analysis, a new perspective has changed the history and future of mankind. This is clearly illustrated in a wide variety of cases, whether it is a “criminal” being freed from prison or the identification of passengers of the Titanic. It has reached a point where it is nearly impossible for someone to not leave physical evidence wherever they go.
For example, in cases where DNA samples do not include sperm and only the identification of the suspect as male is present, Y chromosome analysis can be used to find specific genetic loci specific to an individual. At the present time, labs have the equipment and expertise to look at more than 20 specific DNA loci; however, this number will increase with technological advances. It has been predicted that by the year 2010, one will be able to examine loci that determine physical traits.
Advances in technology may lead to handheld DNA devices for quick identification of a suspect for arrest. Furthermore, a research team consisting of scientists and engineers at the University of Michigan has developed a “lab on a chip” that electronically analyzes DNA samples. This inexpensive glass silicon chip is portable, extremely efficient, and is one of the latest advances in DNA technology.
Furthermore, genetic engineering and cloning have come together to be able to clone animals with specific traits. Once the gene for a particular trait is discovered, then it is only a matter of time before the gene is manipulated to change or eliminate its effect. For example, the gene Fel dl in cats that produces a protein that causes an allergic reaction in humans has been identified. Thus, alteration of that gene may one day help many people who suffer from cat allergies.
The formation of a completed national and world DNA database in the future will be of great assistance in solving crimes. It is certain that the future of DNA testing will continue to ride the wave of technology into the future.
With increasing knowledge and technology, the future of DNA testing will continue to influence mankind. Today, the use of DNA testing in criminal cases and paternal decisions has become widespread. For instance, if it were not for the advancement of DNA analysis, more than half of the World Trade Center victims would not have been identified. In addition, in the war against terror, DNA databases will continue to help track and capture members of al Qaeda, especially Osama bin Laden.
With the latest advances, one can only imagine the impact DNA testing will have on human life over the next century. Researchers have already begun putting missing pieces together to uncover some of the unanswered questions from our past. For example, DNA analyses have already been conducted on U.S. presidents such as Thomas Jefferson and James Madison in an attempt to determine whether they fathered children by female slaves.
The field of genetics is extremely fascinating, with new developments and discoveries happening everyday. However, being able to uncover the “blueprint of life” may also be frightening at times. Depending upon the views of society and the laws of the land, difficult issues that have an impact on individual privacy will continue to arise. As promising as a national database may seem, have we really thought about the ethical implications on members of society? Whether dealing with genetic diseases and biological warfare cases such as anthrax or putting criminals behind bars, DNA testing has and will certainly continue to become an important aspect of humanity.
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