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The icon indicates free access to the linked research on JSTOR.

Lynette White was murdered in 1988. When the three men first imprisoned for her murder were found to have been wrongfully convicted, it seemed that her killer would go unpunished. However, new technology invented in 2002 was used to analyze DNA found at the scene of the murder. The only match was to a boy too young to have committed the murder, but DNA samples were taken from his family. The youth's uncle confessed, and was sentenced to life imprisonment in 2003.

In criminal investigation, DNA evidence can be a game-changer. But DNA is just one piece of the puzzle, rarely giving a clear "he did it" answer. According to a consortium of forensic experts who released a report earlier this year, there are limits to what DNA can tell us about a crime. And what it can and can't reliably prove in court needs to be much clearer.

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DNA (deoxyribonucleic acid) is a code that programs how we will develop, grow, and function. Humans are thought to have DNA that is 99.9% identical, but the remaining 0.1% makes us individuals, marking us out as unique. The fact that humans and chimpanzees have just a 1% difference in their DNA further highlights how meaningful a small difference can be. Generally, the more closely related we are to someone, the more similar our DNA will be to theirs.

The tiny part of our DNA that is unique to us can be used to generate a DNA profile. This profile is usually represented as a graph showing different peaks, which reports the patterns at different points where our DNA is most likely to be unique.

"The increasingly prominent role played by forensic science in the administration of criminal justice is due in no small measure to the meteoric rise in DNA profiling," wrote the law professor Liz Hefferman in a 2008 article for the British Journal of Criminology.

* * *

DNA profiling has had some remarkable successes, including finally ending a two-decade long hunt for the "Green River Killer," who strangled at least fifty women, dumping their bodies in various spots around the Green River in Washington State. However, DNA profiles are often not clean enough to conclusively identify an individual. Ideally, a DNA sample would be complete enough to examine at least 16 different "markers," points at which an individual's DNA fingerprint can be sketched out. But when DNA is damaged, as it often is through exposure to moisture or extreme temperatures, only some of these markers will be available, and forensics teams will generate a partial profile. Put simply, if a DNA profile is a complete description of a person's appearance, a partial profile might describe only one of their traits-hair color, for instance.

Even full DNA profiles may match with a person other than the culprit.

Partial profiles will match up with many more people than a full profile. And even full profiles may match with a person other than the culprit. Further complicating matters, a single DNA profile might be mistakenly generated when samples from multiple people are accidentally combined. It's a messy world.

Realistically, then, DNA profiles should only be thought of as being likely to have come from a specific individual. Statistical approaches such as "match probability," which is based on comparisons between crime scene DNA and a hypothetical "random" person, often are misunderstood. A more rigorous statistical approach is likelihood ratio, which directly compares two hypotheses: the likelihood of the DNA coming from the suspect vs. the likelihood of the DNA coming from someone else. If the likelihood ratio is less than one, the defense position (the DNA is not the suspect's) is better supported; if it is greater than one, there is more support for the prosecution case. Still, the ratio at most provides scientific support for a theory, not a yes-or-no answer.

* * *

A study from the University of California published in Law and Human Behavior tested undergraduate students' abilities to interpret statistical evidence as it would be presented in court by prosecution and defense attorneys. The researchers found that the majority of these undergraduates failed to detect errors in statistical arguments and "made judgements based on fallacious reasoning."

"Telling a jury it is implausible that anyone besides the suspect would have the same DNA test results is seldom, if ever, justified."

When the American Bar Association reported on DNA technology, it backed the use of DNA evidence, but urged caution in how statistics were interpreted. The ABA urged lawyers not to oversell DNA evidence and suggested that courts take the standards of the lab into account when considering DNA evidence. "Telling a jury it is implausible that anyone besides the suspect would have the same DNA test results is seldom, if ever, justified," the report states.

In addition, the European Forensic Genetics Network of Excellence ( EUROFORGEN) and the charity Sense about Science collaborated on a report released earlier this year. The report sought to clarify what DNA analysis can and cannot do within the criminal justice system. EUROFORGEN researcher Denise Sydercombe Court, based at King's College London, said:

We all enjoy a good crime drama and although we understand the difference between fiction and reality, the distinction can often be blurred by overdramatised press reports of real cases. As a result, most people have unrealistic perceptions of the meaning of scientific evidence, especially when it comes to DNA, which can lead to miscarriages of justice.

At times, DNA evidence has been misused or misunderstood, leading to miscarriages of justice. A man with Parkinson's disease who was unable to walk more than a few feet without assistance was convicted of a burglary based on a partial DNA profile match. His lawyer insisted on more DNA tests, which exonerated him. In 2011, Adam Scott's DNA matched with a sperm sample taken from a rape victim in Manchester -a city Scott, who lived more than 200 miles away, had never visited. Non-DNA evidence subsequently cleared Scott. The mixup was due to a careless mistake in the lab, in which a plate used to analyze Scott's DNA from a minor incident was accidentally reused in the rape case.

Then there's the uncomfortable and inconvenient truth that any of us could have DNA present at a crime scene-even if we were never there. Moreover, DNA recovered at a crime scene could have been deposited there at a time other than when the crime took place. Someone could have visited beforehand or stumbled upon the scene afterward. Alternatively, their DNA could have arrived via a process called secondary transfer, where their DNA was transferred to someone else, who carried it to the scene.

Additionally, DNA technology is becoming more and more sensitive, but this is a double-edged sword. On one hand, usable DNA evidence is more likely to be detected than ever before. On the other hand, contamination DNA and DNA that arrived by secondary transfer is now more likely to be detected, confusing investigations. If legal and judicial personnel aren't fully trained in how to interpret forensic and DNA evidence, it can result in false leads and miscarriages of justice.

Another consideration is that people shed DNA at different rates. DNA is found in bodily fluids, such as blood, semen, and saliva, but we also lose microscopic pieces of skin and hair on a regular basis. Some people lose DNA more quickly than others-if they have a skin condition, for example. If a thief uses a particular location as a stash, and a caretaker who suffers from eczema stumbles on it and reports it to the police, the forensics alone might implicate the caretaker. The quantity of their DNA present might suggest a significant period of time spent at that place. But in fact, the caretaker's eczema resulted in more DNA being deposited there over a shorter time period.

National DNA databases, then, present some ethical quandaries. Many cases would never have been solved if not for DNA databases. In the Lynette White case, the breakthrough came when the police obtained the DNA profile of a relative of the murderer. However, the retention of DNA details raises legitimate privacy concerns, especially in the context of familial searching. Partial matches are more likely to lead to false positive identification of suspects who are already in the DNA database. Given that less privileged groups tend to be over-represented in DNA databases, this is a serious issue.

In 2011, a group of scientists asked whether forensic DNA databases increase racial disparities in policing. They pointed out that, in the U.S., different communities are differently policed, leading to different rates of incarceration and DNA recording. According to the study authors, actual drug use is relatively higher in white communities, but "buy and bust" operations by police are more common in African American and Latino communities, leading to disproportionate arrests.

The lesson of all this research: DNA evidence is a powerful tool in criminal investigation and prosecution, but it must be used with care. It should never be oversold in court, and it should only ever be considered in light of other available evidence. For example, if DNA is recovered in a kitchen that has been broken into, it could be from the homeowner, their guests, or even a member of the CSI team (if sufficient care hasn't been taken to avoid contamination). If a tool-mark impression reveals that a screwdriver was used to force open the window, and DNA is recovered from a screwdriver found at the scene that does not belong to the homeowner, that's incriminating. If that DNA is a partial or full match with an individual with the same shoe size as a footprint left in the grass under the window, even more so. If that individual has a torn piece of clothing that matches cloth fibres snagged in the window, that's more incriminating still. If digital evidence such as their mobile phone records place them at the scene at the time the break-in happened-even though they claim to have been elsewhere-then you have a more complete picture.
Editor's notes: An earlier version of this story contained an unclear reference to evidence seized by police investigating the murder of Meredith Kercher. The example has since been removed. We regret any error.
A study cited in an earlier version of this article is no longer available for free on JSTOR.

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How Forensic DNA Evidence Can Lead to Wrongful Convictions - JSTOR Daily

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Forensic DNA evidence has been a game-changer for law enforcement, but research shows it can contribute to miscarriages of justice.

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https://doi.org/10.1038/d41586-018-05029-9

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The ethics of catching criminals using their family’s DNA

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A high-profile arrest in California shows how the long arm of the law can now extend into DNA databases to check for relatives.

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https://www.youtube.com/watch?v=KT18KJouHWg&t=1s&ab_channel=Veritasium

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https://online.maryville.edu/blog/how-is-dna-profiling-used-to-solve-crimes/

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DNA profiling is a state-of-the-art procedure that can be used to identify individuals on the basis of their unique genetic makeup. While people may share the same eye and hair color, and may even have similar facial features, they will not have the same DNA. This means the process can be useful in more accurately solving crimes. Forensic scientists can compare DNA found at a crime scene (from blood or hair, for example) to DNA samples taken from suspects. If there is no match, they may be able to rule out that suspect. If there is a match, police will likely want to take a closer look.

Such technology has revolutionized the criminal justice system over the past decades, increasing the likelihood of identifying criminals with virtual certainty. This can make it not only easier to identify perpetrators, but just as importantly decreases the odds of mistakenly putting innocent people behind bars.

In some cases, advances in DNA profiling have allowed law enforcement professionals to solve decades-old cases based on samples of DNA-rich material (such as fingernail clippings) collected before DNA testing was possible.

In other cases, a DNA profile may have been created at the time of the crime, but no match was found during the initial criminal investigation. This problem is now easier to overcome thanks to current database technology, which allows for DNA profiles to be stored and quickly searched. Alternately, DNA profiling advances have also enabled law enforcement to exonerate people who were wrongfully convicted of crimes they didn't commit.

The road to modern DNA profiling has been long, and it has taken forensic scientists decades of work and fine tuning to develop the highly accurate testing and analysis procedures available today. This article examines how current methods for DNA profiling came to be, and explains the procedure's current role in the contemporary criminal justice system, including its risks and benefits.

While DNA is one important factor in solving crimes, it is not the only one. Other aspects of criminal investigation - such as forensic psychology - remain an integral part of the process when it comes to capturing offenders. We'll also explore the role of forensic psychologists, their impact on criminal justice, and the profession's career outlook.

What Is DNA?

Before diving into the details of DNA profiling, it's important to understand what DNA is. Each person has unique DNA, an acronym that stands for deoxyribonucleic acid - the essential building block of the body's cells. DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). How these DNA bases are sequenced and organized in an organism's genome, a kind of genetic blueprint, provides cells with the information needed to build an organism.

Each cell in the body has a nucleus, an inner core, which holds chromosomes. DNA molecules make up these chromosomes. The chromosome contains "markers" - points that repeat short DNA sequences again and again. Just how many times a sequence repeats at each marker varies depending on the person. Every person has two copies - called alleles - of each marker: one from the mother's side and another from the father's. Forensic scientists can use so-called short tandem repeats (STRs) of DNA to identify individuals.

Because DNA is hereditary, DNA testing is often used in legal cases to determine maternity or paternity - for instance, when child custody and child support issues are at stake. As the U.K. National Health Service explains, scientists can compare the DNA of two persons using a blood test or even a saliva swab taken from the inside of the cheek. DNA testing can even be performed before a child is born, using tissue taken from the placenta or a sample of the amniotic fluid surrounding the child in the womb. This type of test can also be used to check for genetic abnormalities indicative of illnesses and diseases.

DNA is not just a unique personal identifier, but it can also reveal details about a person's heritage. Advances in DNA technology have allowed for the surge of at-home genealogy kits that provide people with information about their possible genetic background. Companies like 23andMe and Ancestry.com sell do-it-yourself DNA kits, which are delivered to the consumer's front door. The person provides a saliva sample and sends it back to the company, which analyzes the individual's ancestry.

For instance, a consumer DNA kit might identify a person's DNA shares key components with traditionally West African DNA, as the Live Science article "How Do DNA Ancestry Tests Really Work?" explains. The rise of DNA-driven genealogy databases is also one trend that has supported the increased use of DNA profiling in the criminal justice system.

What Is DNA Profiling?

The first step in DNA profiling is to procure relevant DNA samples. Only a small number of cells from a person's skin or the root of a hair - or from bodily fluids like blood, saliva, or semen - is needed to build a unique DNA profile. DNA is often discovered at crime scenes during police investigations, after which persons of interest may be asked to voluntarily provide their DNA sample. If there is a strong body of evidence against a suspect, the courts can order them to provide a DNA sample.

Once forensic scientists obtain a sample, they extract the DNA from cells in bodily fluids or tissues and copy it. They then separate the copied markers using a process known as capillary electrophoresis. This enables them to identify distinct markers and the number of repeats for different markers in each allele. The forensic scientists read this data using a chart called an electropherogram, which plots fragments of DNA and shows how many repeats there are for each marker and where they occur. Based on this chart, forensic scientists generate a DNA profiling definition that law enforcement professionals can read. This definition consists of a simple list of numbers, indicating how many repeat units are in each allele of 20 marker points throughout the person's genome.

Examples of Types of DNA Profiling Cases

The first recognized case of DNA profiling in the forensic science community was that of Colin Pitchfork. In 1986, a girl named Dawn Ashworth was sexually assaulted and murdered in Leicester, England. A man named Richard Buckland confessed to the crime, but police were not confident that he was the killer. They approached Alec Jeffreys, a genetics professor at the University of Leicester, for help. Jeffreys had previously discovered that each person's DNA exhibited distinct patterns that could be used to distinguish one person's DNA from another's. Jeffreys compared DNA from the crime to Buckland's, and as police had suspected, it did not match.

Jeffreys went on to analyze over 4,000 DNA samples voluntarily provided by men in the Leicester area who wanted to clear their names and help find the perpetrator. Still, no match was found. Then one man confessed that he had been paid to provide a false sample on behalf of the actual perpetrator - a man named Colin Pitchfork. When Pitchfork's DNA was checked, it matched the DNA at the crime scene. He was sentenced to life in prison in January of 1988.

DNA profiling can also be used to exonerate the wrongfully convicted. For instance, 70-year-old Craig Coley was freed from a California prison in 2017 after DNA testing cleared him of a double-murder he had been convicted of 1978.

Coley had been sentenced to life in prison without parole. Throughout his trial and afterward, he had always maintained his innocence. When biological samples from the crime scene were retested in 2015, the results showed the DNA at the crime scene did not match Coley's - and that other people's DNA was present. According to area police, the technology for testing the crime scene DNA sample wasn't available in the 1970s when Coley was convicted. Reuters reports that Coley is one of more than 350 people exonerated in the U.S since 1989 thanks to DNA testing.

The History of DNA Profiling

It has taken forensic scientists years to develop the highly accurate testing procedures that make examples like those above possible. Today's processes rely on the aforementioned STRs, short tandem repeats. A single STR used in today's forensics is some three to five DNA bases in length. In the past, much longer repeat segments of bases were required, measuring from hundreds to even tens of thousands. Also in the past, when DNA was isolated and separated into fragments, it was labeled using radioactive phosphorus and then examined using X-ray-sensitive film. The entire process took anywhere from six to eight weeks.

Today, the process is more streamlined thanks to the switch to STRs. Another advance that has made DNA profiling more efficient is the transition from gel electrophoresis to capillary electrophoresis to separate DNA. Gel electrophoresis can't withstand electric fields of more than 40V, while capillary electrophoresis can apply voltages of up to 30,000V, reducing separation time to mere minutes instead of hours.

Additionally, DNA analysis has advanced greatly due to the development of a technique known as polymerase chain reaction, or PCR. This process involves heating and cooling DNA samples in cycles, ultimately "amplifying" the DNA and making fragments easier to detect. With this development (which was ultimately recognized with a Nobel Prize, a landmark moment in DNA profiling history) forensic scientists are able to work with smaller amounts of biological evidence.

Previously, a bloodstain for example, would have to be at least the size of a dime or quarter to elicit enough DNA for a profile. With PCR, profiling is possible with even smaller amounts of blood. Today's DNA profiling is more sensitive. As a result, investigators can often retrieve DNA from minute numbers of skin cells left behind by a criminal. They can even distinguish the DNA of multiple individuals (for instance, if many people touched the same surface).

The DNA Profiling Process Today

Such advances in the technologies and processes used to collect and analyze DNA are just part of what makes advanced DNA profiling so useful. Another aspect is the rise of database technology. When law enforcement professionals can comb through large volumes of DNA data stored in computer databases, they have better odds of finding matches for material collected at crime scenes.

The Federal Bureau of Investigation (FBI), for example, relies on the Combined DNA Index System, or CODIS, which uses computer and DNA technologies to compare DNA profiles. It can generate investigative leads in scenarios where biological evidence, such as semen or blood, has been recovered from a crime scene. Each CODIS profile has a specimen identifier, the processing lab's identifier, and the actual DNA profile. Law enforcement in different jurisdictions can use CODIS to coordinate distinct investigations and share leads. Matches generated via CODIS allow law enforcement to pinpoint a suspect's identity.

In recent years, the criminal justice system has also turned to other types of databases - genealogy databases - to identify suspects. As mentioned before, private companies sell at-home DNA testing kits, which people can use to discover more about their genetic history. These companies often encourage users to upload their data for genealogical purposes. This enables them to more readily identify connections, even putting them in touch with distant relations.

In Spain, a woman who was taken from her biological parents as a baby under the Franco dictatorship found her biological family through such a DNA database. In some cases, police can also comb through these files for DNA profiling purposes, searching for individuals who may be criminal suspects or related to suspects.

In 2019, for instance, a 35-year-old cold case murder in Wisconsin was solved using DNA and genealogy databases. Following the 1984 rape and murder of a woman in Milwaukee, police were able to compose a DNA profile of the perpetrator based on semen found at the crime scene. There was no known suspect at the time, however, so police were unable to find a match for the sample. Decades later, police began searching through genealogy databases, which hold millions of DNA profiles, thinking they might find someone who was related to the perpetrator. They identified one individual who turned out to be the killer's second cousin. Through this family connection, they were able to trace the family tree and find the killer, whose DNA was a match with the sample collected from the crime scene over 30 years prior.

DNA Profiling Uses in the Criminal Justice System

These examples highlight some of the primary uses of DNA profiling in today's legal system. The process can be used to identify potential suspects and link suspects to a crime, proving they were at a certain place. DNA profiling also enhances the criminal system's accuracy. Eyewitness accounts are unreliable, particularly in high-pressure situations during the commission of a crime. In the article " The Neuroscience of Memory: Implications for the Courtroom," researchers note that memory distortions can cast doubt on eyewitness testimony. By comparison, DNA is scientifically accurate and thus more difficult to dispute.

It's clear that advances in DNA collection and analysis, combined with the power of DNA technology, have in many ways transformed the criminal justice system. However, it's important to note that although DNA profiling is highly accurate and can play a big role in catching criminals, it's only one part of the overall criminal justice process.

It takes more than DNA to convict a person of a crime. Forensic psychology remains an integral part of the process, for example. This application of psychology in the legal field is central to deepening law enforcement's understanding of criminal behavior. Forensic psychologists can help answer questions such as who committed a crime and why. It can also help discern why a person committed a crime in a certain manner - for instance, by opting for a particular weapon. Forensic psychologists also deal with the impact of crimes on victims and may work in victim advocacy.

DNA Profiling Pros and Cons

Although DNA profiling undoubtedly has many practical uses, there are some drawbacks. Questions have already been raised about the ethical implications of catching criminals based on searches of their family's DNA (as exemplified in the Wisconsin case noted earlier). Nature, the weekly scientific magazine, highlights a number of such instances and the fact that most people who use genealogy databases are unaware that law enforcement may be able to subpoena their information.

There are also ethical and privacy concerns when it comes to law enforcement storing DNA data from convicted criminals. Storing an individual's DNA, even if they have been convicted of a crime, can be seen as a violation of a basic human right to privacy.

The MIT Technology Review even goes so far as to call large-scale databases like those used to find the Golden State Killer a "national security leak waiting to happen." Unlike a credit card, which can be replaced, a person's genome can't be. The article argues that foreign intelligence could grab millions of American DNA profiles from a database and potentially use the information to identify the true identities of American diplomats or spies and their relatives. They could also pinpoint political information that could potentially be compromising. While this has yet to happen as far as we know, the possibility is very real. The technology is there, and so is the data.

Another concern with DNA profiling is the procedure itself. Although very accurate, it is not 100% foolproof. A partial DNA profile (one that is not complete), for example, may match with multiple people and should not serve as conclusive evidence.

DNA can also be abused, misused, or misunderstood, causing miscarriages of justice. In 2011, a careless lab error resulted in an innocent man being charged with rape because his DNA was erroneously found to match a sperm sample taken from the victim. It later became clear that the lab had mixed up its files. In short, DNA is just one piece of the criminal justice puzzle, and should not be relied on to the exclusion of other investigative and analytical tools.

Criminal Justice Beyond DNA - The Value of a Degree in Forensic Psychology

The cutting-edge science of DNA profiling requires professionals to work in laboratory settings that are removed from evidence collection and apart from the human element of criminal justice. While their work is an integral part of the modern criminal justice system, many who are interested in justice-related careers may be drawn to other specialties.

Consider forensic psychology, which provides the opportunity to examine crime as it relates to the human psyche in the cases of both perpetrators and victims. Those in the field may work to pinpoint future indicators of violent behavior, for example, or help victims through advocacy support. As a career, psychology as a whole is a growing field, with the U.S. Bureau of Labor Statistics (BLS) predicting a growth rate of 14% between 2018 and 2028.

Individuals who are interested in learning more about forensic psychology would do well to explore Maryville University's online BA in Forensic Psychology. The program covers both psychology core curricula, from social psychology to cognition, as well as criminal justice coursework covering everything from juvenile delinquency to multicultural issues. Students are further encouraged to gain practical experience through an internship, enabling them to understand the connection between course material and its real-world application.

This Maryville University online BA offers a comprehensive mixture of both theoretical and practical teaching. This approach is designed to prepare students for rewarding careers in a number of roles - in police departments or medical laboratories, working with parolees and probation offices, excelling as victim advocates, and beyond. The curriculum also provides a strong foundation for those interested in pursuing further education to become forensic psychologists.
If you're drawn to a career in criminal justice that performs beyond the lab - and takes into account the human condition - explore Maryville University's online BA in Forensic Psychology program today.
Recommended Reading BA Forensic Psychology Careers How to Become a Forensic Psychologist An Introduction to the World of Forensic Psychology Sources Chemical and Engineering News, "Thirty Years of DNA Forensics: How DNA Has Revolutionized Criminal Investigations" The Guardian, "DNA Database Helps one of Spain's 'Stolen Babies' Find Family" Investigative Genetics, "DNA Fingerprinting in Forensics: Past, Present, Future" JSTOR Daily, "How Forensic DNA Evidence Can Lead to Wrongful Convictions" Live Science, "How Do DNA Ancestry Tests Really Work?" The Malaysian Journal of Medical Sciences, "Forensic DNA Profiling and Database" MIT Technology Review, "The DNA Database Used to Find the Golden State Killer Is a National Security Leak Waiting to Happen" National Review of Neuroscience, "The Neuroscience of Memory: Implications for the Courtroom" Nature, "The Ethics of Catching Criminals Using Their Family's DNA" NBC News, "35-Year-Old Cold Case Murder in Wisconsin Solved Using DNA and Genealogy" Reuters, "After DNA Test, California Man Freed From Prison in 1978 Double-Murder" The U.S. Bureau of Labor Statistics Occupational Outlook Handbook, "Psychologists" U.K. National Health Service, "What Is a Prenatal Paternity Test?" U.S. National Library of Medicine, What Is a Chromosome?" U.S. National Library of Medicine, "What Is DNA?"

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DNA Profiling: How Is It Used in Criminal Justice?

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DNA profiling is a state-of-the-art procedure that can be used to identify individuals on the basis of their unique genetic makeup. While people may share the same eye and hair color, and may even have similar facial features, they will not have the same DNA.

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https://theconversation.com/dna-is-often-used-in-solving-crimes-but-how-does-dna-profiling-actually-work-191937

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DNA profiling is frequently in the news. Public interest is sparked when DNA is used to identify a suspect or human remains, or resolves a cold case that seems all but forgotten.

Very occasionally, it is in the media when the process doesn't work as it should.

So what is DNA profiling and how does it work - and why does it sometimes not work?

Read more: Australia has 2,000 missing persons and 500 unidentified human remains - a dedicated lab could find matches

A short history of DNA profiling

DNA profiling, as it has been known since 1994, has been used in the criminal justice system since the late 1980s, and was originally termed "DNA fingerprinting".

The DNA in every human is very similar - up to 99.9% identical, in fact. But strangely, about 98% of the DNA in our cells is not gene-related (i.e. has no known function).

This non-coding DNA is largely comprised of sequences of the four bases that make up the DNA in every cell.

But for reasons unknown, some sections of the sequence are repeated: an example is TCTATCTATCTATCTATCTA where the sequence TCTA is repeated five times. While the number of times this DNA sequence is repeated is constant within a person, it can vary between people. One person might have 5 repeats but another 6, or 7 or 8.

There are a large number of variants and all humans fall into one of them. The detection of these repeats is the bedrock of modern DNA profiling. A DNA profile is a list of numbers, based on the repeated sequences we all have.

The use of these short repeat sequences (the technical term is " short tandem repeat" or STR) started in 1994 when the UK Forensic Science Service identified four of these regions. The chance that two people taken at random in the population would share the same repeat numbers at these four regions was about 1 in 50,000.

Now, the number of known repeat sequences has expanded greatly, with the latest test looking at 24 STR regions. Using all of the known STR regions results in an infinitesimally small probability that any two random people have the same DNA profile. And herein lies the power of DNA profiling.

How is DNA profiling performed?

The repeat sequence will be the same in every cell within a person - thus, the DNA profile from a blood sample will be the same as from a plucked hair, inside a tooth, saliva, or skin. It also means a DNA profile will not in itself indicate from what type of tissue it originated.

Consider a knife alleged to be integral to an investigation. A question might be "who held the knife"? A swab (cotton or nylon) will be moistened and rubbed over the handle to collect any cells present.

The swab will then be placed in a tube containing a cocktail of chemicals that purifies the DNA from the rest of the cellular material - this is a highly automated process. The amount of DNA will then be quantified.

If there is sufficient DNA present, we can proceed to generate a DNA profile. The optimum amount of DNA needed to generate the profile is 500 picograms - this is really tiny and represents only 80 cells!

How foolproof is DNA profiling?

DNA profiling is highly sensitive, given it can work from only 80 cells. This is microscopic: the tiniest pinprick of blood holds thousands of blood cells.

Consider said knife - if it had been handled by two people, perhaps including a legitimate owner and a person of interest, yet only 80 cells are present, those 80 cells would not be from only one person but two. Hence there is now a less-than-optimal amount of DNA from either of the people, and the DNA profiling will be a mixture of the two.

Fortunately, there are several types of software to pull apart these mixed DNA profiles. However, the DNA profile might be incomplete (the term for this is "partial"); with less DNA data, there will be a reduced power to identify the person.

Worse still, there may be insufficient DNA to generate any meaningful DNA profile at all. If the sensitivity of the testing is pushed further, we might obtain a DNA profile from even a few cells. But this could implicate a person who may have held the knife innocently weeks prior to an alleged event; or be from someone who shook hands with another person who then held the knife.

This later event is called "indirect transfer" and is something to consider with such small amounts of DNA.

Read more: Criminals can't easily edit their DNA out of forensic databases

What can't DNA profiling do?

In forensics, using DNA means comparing a profile from a sample to a reference profile, such as taken from a witness, persons of interest, or criminal DNA databases.

By itself, a DNA profile is a set of numbers. The only thing we can figure out is whether the owner of the DNA has a Y-chromosome - that is, their biological sex is male.

A standard STR DNA profile does not indicate anything about the person's appearance, predisposition to any diseases, and very little about their ancestry.

Other types of DNA testing, such as ones used in genealogy, can be used to associate the DNA at a crime scene to potential genetic relatives of the person - but current standard STR DNA profiling will not link to anyone other that perhaps very close relatives - parents, offspring, or siblings.

DNA profiling has been, and will continue to be, an incredibly powerful forensic test to answer "whose biological material is this"? This is its tremendous strength. As to how and when that material got there, that's for different methods to sort out.

Read more: New technology lets police link DNA to appearance and ancestry - and it's coming to Australia

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DNA is often used in solving crimes. But how does DNA profiling actually work?

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DNA profiling is frequently in the news. Public interest is sparked when DNA is used to identify a suspect or human remains, or resolves a cold case that seems all but forgotten. Very occasionally, it is in the media when the process doesn't work as it should.

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Questions Answered in the Research/Report

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Questions Answered in the Research/Report

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- What is DNA profiling and when was it invented?
- What is it used for?
- How has it revolutionized crime detection/forensic science?
- Is DNA profiling successful?
- How useful/effective is this technology in fulfilling its purpose?
- What are its advantages & disadvantages?
disadvantages
- What are the ethical concerns about DNA profiling?
- Advantages of DNA databases
- Where does all the data of our DNA get stored?
- Who has access to our DNA data?
- How have the ethical implications affected the public's perception of law enforcement in the US (mainly from 2018 onwards)?
- Case study of the Golden State Killer

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- The method used by investigators to identify the serial killer was controversial because of the law enforcements' use of DNA databases for this criminal investigation

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- Security risks: The DNA database (GEDMatch) used for the investigation had lax security measures but it had thousands of DNA profiles, so searching for the DNA profile of a specific person was possible even without having access to the database itself
- Privacy concerns: Because of how genealogies of families were used without their consent during this investigation

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Used for identifying suspects in criminal investigations
- Highly valuable & successful tech

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DNA Profiling - Synonym of DNA fingerprinting
DNA Database - Where the DNAs of people are stored

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With DNA profiling revolutionizing crime detection and forensic science, it has lead to various successful outcomes including the arrest of the Golden State Killer. However, the methods used by law enforcements in order to capture the criminal has raised many public concerns and debates regarding the government and law enforcement’s usage of DNA profiling and DNA databases. The ethical implications of said topic has long existed since the past, but ever since it has been brought into question by the public since the incarceration of the infamous killer, the public’s views and perceptions on the government and law enforcements have been impacted.