How do we know that everybody's DNA fingerprint is unique?

How do we know that everybody's DNA fingerprint is unique?

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How do we know that everybody's DNA fingerprint is unique?

I know, I know, everybody's DNA is unique.

But when we do DNA fingerprinting, we're looking at very specific regions of high variability.

How do we know that just by chance, two people's DNA could be the exact same in the spot(s) we're observing.

With real fingerprints, uniqueness is (almost) guaranteed (I believe it's a 1 in 64 billion chance) because they are developed by physical stresses on the fetus in the womb.

Is there any similar mechanism/affect that acts on these non-coding/highly variable sections of DNA?



First, remember that identical twins actually have the same genotype. So its not exactly true that everyone has a unique genome.

But to get at the heart of it, you're asking how I can be sure that I have a different genome than you, or even than say my brother. And moreover you're asking how these differences are obvious enough that they can be detected without whole genome sequencing.

The answer is that there is no mechanism to ensure differences, but that the differences arise from the enormous variability of our genome. Look at the major histocompatibility complex, or MHC, a cluster of genes that affect our immune system.

Just to simplify things, lets focus in on four genes in this cluster: HLA-A, HLA-B, HLA-C and HLA-DRB1. According to this site there are 2579, 3285, 2133 and 1411 alleles for each, respectively. If we make a naive assumption that each of us received a random assortment of these genes, that makes 2579 x 3285 x 2133 x 1411 = 25,549,791,000,000 possible combinations. The chance that we both have the same combination is then about 1 in 25 trillion, just considering 4 genes.

But wait, you say, surely some of these genes are not equally likely and surely they segregate together, making this chance much smaller. You would be right. But this consideration stops mattering very much when you account for the rest of the variable regions. They combine multiplicatively, so considering a fifth gene with only 2 possible alleles brings the possible combinations to 50 trillion.

If you consider just a few more genes, the numbers get unthinkably high. This pretty much ensures that, even considering a small sequence, we can be sure that the genetic fingerprint is unique.

Possibly partly offtopic, but I'd like to add that when using dna fingerprint as evidence of identity in a legal investigation, the odds become smaller due to combination of human factors and reduced accuracy. There is the twin issue already mentioned, but in addition there are laboratory errors and the possibility of contamination with other evidence. Samples may be damaged in other ways as well, and dna samples can be planted.

In the analysis done by Jonathan Koehler, it was found that around 1.2% of tests used in this context gave out an incorrect match. Additionally, in this other study by him it was found that the way results are presented has a considerable impact as well.

We get our DNA from our parents. So how are we all unique?

When talking about DNA and how people inherit different traits, you’ll probably come across the term recombination—a critical process in human genetics that ultimately helps give you a diverse genome with bits of DNA from both your ancient and recent ancestors. Understanding recombination will help you learn about human inheritance, and discover some of the processes that helped make you uniquely you.

Human DNA is 99.9% identical from person to person. Although 0.1% difference doesn’t sound like a lot, it actually represents millions of different locations within the genome where variation can occur, equating to a breathtakingly large number of potentially unique DNA sequences. But how can nearly everyone have a unique DNA sequence if we inherit our DNA from our parents? Wouldn’t it stand to reason that our DNA is the same as theirs? In short, the answer is no.

There are multiple ways our bodies ensure that we have a unique set of DNA that differs from our parents. For starters, you inherit two copies of each chromosome—one copy from your mom and one copy from your dad. This means that your genome (all of your DNA) is already different because it contains chromosomes from both of your parents. This can also help explain why two siblings appear to have different genetic ancestry, since they may get different chromosomes from their parents.

But there is more to the story than the combination of chromosome pairs. The actual sequence of DNA on each of the chromosomes is unique due in part to recombination. To understand this, we have to talk about the process of making gametes, which are also known as sperm or egg cells. One of the traits that makes gametes different from all other cells in your body is they only have one copy of each chromosome,making a total of 23 chromosomes this is in contrast to most other cells in the body which have two copies of every chromosome, giving them a total of 46. The body does this to make sure that a fertilized egg has the right amount of chromosomes—23 donated from the egg, and 23 donated from the sperm to give a total of 46.

Gametes are made from a special kind of cell dedicated to producing either sperm or eggs. When making the sperm or egg, cells will arrange their chromosomes next to each other, making sure that each chromosome is next to its respective copy. It’s at this point that recombination can happen.

Recombination is a process where sections of DNA are traded between the chromosomes that make up a pair. For example, chromosome 1 from your biological mother will be lined up next to chromosome 1 from your biological father. After recombination, the chromosomes will look somewhat like a quilt because they are made up of DNA from both parents (this process is depicted in the figure below). An important point to note here is that the total amount of DNA on each chromosome should not change in a significant way, because a portion of your mom’s chromosome was traded for the same portion on your dad’s chromosome.

This figure depicts six chromosomes (three pairs, each pair inherited from the person’s parents). Note that recombination only occurs in special cells that generate gametes. Shortly after recombination, the chromosome pairs will be seperated and sex cells will be formed.

So if the chromosomes are trading the same sections of DNA, how does this create a unique sequence? The human DNA sequence consists of nearly 3 billion DNA base pairs. The order or these base pairs is nearly identical from person to person, but sometimes there are random changes in the sequence. We call these changes variants. The combination of all of your variants make up the 0.1% difference in your DNA—the part of your DNA that makes you unique from everyone else—and helps give you a unique sequence. This means when chromosome pairs come together, the chromosomes you inherit from your mom are slightly different from the chromosomes you inherit from your dad thanks to the many DNA variants on each of the chromosomes.

When recombination happens, the chromosomes are essentially trading DNA variants amongst themselves. This process helps drive evolution by creating a slightly new version of the DNA, which may give your offspring a competitive advantage by giving you variants that help you better metabolize nutrients or blend in with your environment, for example. (Blending in with the environment isn’t very important for modern humans, but for many organisms, it is!)

Each chromosome you have is a unique quilt of DNA, representing segments of the genome that have been passed down from generation to generation, occasionally being shuffled amongst chromosome pairs. This shuffling has helped drive evolution through time, and ultimately has helped write your genome—and the story of you. DNA-based ancestry products (like those offered in the Helix Store) look at these quilted patterns in your DNA to help them trace your genetic heritage back thousands of years, and ultimately help you understand the rich history that lays within your DNA.

Pros and Cons of DNA Fingerprinting

DNA fingerprinting, also referred to as DNA profiling, has nothing to do with fingerprints at all. It is the practice of collecting DNA material, such as hair or blood, and storing the information in a data bank. This is used to identify people in future crimes that they may be associated with. Many people have raised eyebrows about this, does it violate our personal rights to data store our DNA? There are both pros and cons associated with DNA fingerprinting, let’s explore what they are.

The Pros of DNA Fingerprinting

Solving Crimes
Identification is made much easier with the practice of DNA fingerprinting, this is especially true for solving crimes. Instead of having to hope for a match in the already existing databases, it is a guarantee that if DNA is found at a crime scene, they will know who it belongs to.

Reversing Wrongful Convictions
Many people are convicted on circumstantial evidence that are, in fact, innocent of the crimes they are accused of. With DNA fingerprinting, the real culprits can be found so that the people wrongfully imprisoned may be freed of their charges.

The Cons of DNA Fingerprinting

Violation of Privacy
Many people strongly believe that the use of DNA fingerprinting to store identifiable information about citizens is a violation of privacy and our civil liberties.

Strong Sway Over Juries
DNA evidence is huge when it comes to jury trials. It gives, what most people believe, undeniable evidence to convict a person. This could be used in many negative ways, including the planting of DNA evidence at crime scenes.

DNA material holds quite a bit of information about us. The way we look, our genetics, diseases we may have, and many other things. This could be used in multiple negative ways by corporations, potential employers, and other organizations to profile and discriminate before even meeting us.

Against Our Will
If mandatory DNA fingerprinting where to be implemented, that would mean it would be done to everybody, with no exceptions. Baby’s that are born would have a DNA sample collected at the hospital right after they where born, giving them no option to the matter.

15 Unique Facts About Fingerprints

They've been with you since before you were born, but how much do you really know about the lines and ridges on your fingers, palms, and feet?


Human skin has several layers, and each layer has sub-layers. A developing fetus is constantly straining and stretching these layers, which can snag on each other. Scientists believe fingerprints form when the bottom layer of the epidermis grows at a different rate than the rest of the skin, causing it to buckle and tug on the dermis. Your fingerprints are made up of several skin layers twisted together [PDF], kind of like a soft-serve swirl.


Image Credit: Jebulon via WikimediaCommons // CC0 BY 1.0

Alphonse Bertillon was a French policeman and researcher who capitalized on the fact that each person’s body proportions are different. He developed a way of using photographs to measure a person’s unique dimensions—a technique that’s still reflected in jailhouse mug shots. The Bertillon System, as it came to be known, was adopted by law enforcement agencies in Europe and North America and used for three decades.


Three genetic conditions can prevent fingerprints from forming: Naegeli-Franceschetti-Jadassohn syndrome (NFJS), Dermatopathia pigmentosa reticularis (DPR), and adermatoglyphia. NFJS and DPR cause a range of symptoms, most much worse than smooth fingers. Adermatoglyphia, on the other hand, has just one indicator: no fingerprints. It’s sometimes referred to as “immigration delay disease,” for the trouble it causes people trying to cross borders.


In 1901, a man named William West began a life sentence in the Leavenworth, Kansas, penitentiary for murder. His Bertillon measurements were taken and dutifully cataloged. Two years later, Will West entered Leavenworth. When asked if he’d been there before, he said no, but the clerk took his measurements and photograph and found that they were an exact match for the man listed as William West who was currently in the prison. Befuddled, the clerk compared Will’s fingerprints with William's and found that, indeed, they were two completely different men. The story is still a matter of debate—some think the men might have been twins—but it soon became folklore among forensic scientists, illustrating not only the advantages of fingerprinting but the fatal flaws that would lead to the abandonment of the Bertillon system.


When examining fingerprints, experts attempt to match as many points of comparison as possible, but there’s no minimum for a match, at least not in the United States. Other countries have set standards for what constitutes a positive identification, but not us. On top of that, there’s an inevitable element of human error. A 2011 study [PDF] found a false positive rate of 0.1 percent. That may not sound like much until you realize that 0.1 percent of the FBI’s annual fingerprint intake is 60,000 people, or 60,000 potential false positive IDs.


So far, we’re aware of only a few non-human animals with unique fingerprints, such as gorillas, chimpanzees, and koalas. Given apes’ and koalas’ arboreal lifestyles, scientists suspect fingerprints evolved as a consequence of living in trees. The fingerprints of koalas are so similar to humans’ that even experts have trouble telling them apart. We haven’t heard of anyone blaming their misdeeds on a koala yet, but it’s probably just a matter of time.


Even in death, our fingerprints stick around, which makes them very helpful in identifying bodies. Or fingers, in the case of Hans Galassi. After losing a few fingers in an accident on the water, the wakeboarder figured they were gone for good. Then a human finger turned up in the belly of a trout and, sure enough, it was one of Galassi’s. “If a hand is found in water you will see that the epidermis starts to come away from the dermis like a glove,” fingerprint expert Allen Bayle told the BBC. “This sounds gruesome, but if a hand has been badly damaged, I cut the epidermis off and put my own hand inside that glove and try to fingerprint it like that.” (Once the severed finger had been identified, it was offered to Mr. Galassi, who declined to take it back.)


Rough tactile work like bricklaying and chemotherapy drugs like capecitabine can erode and even erase fingerprints. “Just a good case of poison ivy would do it," forensics expert Edward Richards said in Scientific American. Don’t get too worried: "Left alone,” he said, “your skin replaces at a fairly good rate, so unless you've done permanent damage to the tissue, it will regenerate."


By the 1930s, fingerprint analysis was standard practice in U.S. law enforcement, and criminals had begun intentionally trying to remove their fingerprints. As you might imagine, the results were grisly and mixed. Some tried to file off their prints, while others attempted to cut them out. Notorious gangster John Dillinger burnt his own prints off with acid, a hardcore decision that kind of worked. (His fingerprints were never used against him, but after his death the faint traces of his former ridges and whorls could still be seen.) Robber Robert Phillips talked a doctor into grafting skin from his chest onto his fingertips. Unfortunately for him, he neglected to remove the prints on his palms.


Apple created quite a buzz in 2013 when it introduced a fingerprint-coded screen lock with the iPhone 5s. Some of that buzz soon focused on cats, however, after a TechCrunch writer “commandeer[ed] a cat” and used its toe pad to create a new profile. “The cat’s paw worked,” he wrote, “and while it encountered more frequent failures than did a fingerprint, it was able to unlock the phone again repeatedly when positioned correctly on the sensor.”


Two of the author’s books, Life on the Mississippi and Pudd’n Head Wilson, feature the use of fingerprints to nab criminals. Twain’s focus on fingerprinting was incredibly prescient the books were published in 1883 and 1893, respectively, but U.S. officials wouldn’t implement fingerprinting practices here until the early 20th century.


Wartime vigilance meant that the FBI was collecting more prints than ever before, from soldiers, foreign agents, and military suppliers, as well as draft dodgers and potential spies. By 1943, the collection included more than 70 million prints. To manage the explosion of information, the agency moved to a big warehouse (nicknamed the “Fingerprint Factory”) and hired and trained thousands of women to sort prints 10 hours a day, six days a week.


In desperate times, British police have resorted to desperate measures. The shocking murder of a three-year-old girl in 1948 inspired officials to demand prints from more than 40,000 local men. Even with all those prints, they failed to find a match—until they tracked down the 200 men who had failed to produce prints. Among them, they found their culprit. Since then, despite protestations from Britain’s National Council for Civil Liberties, the police have conducted several mass print collections, several of which were successful.

That sort of thing doesn’t go over too well in the United States, but it has been done. The Fourth Amendment restricts the use of fingerprint collection to “reasonable” identification of persons of interest in criminal cases. Law enforcement officers could get around this if they chose, but it wouldn’t be a popular move.


If you’ve ever applied for a teaching job, the police force, or any government position, the FBI has your fingerprints—and they’re treating them like a criminal’s. In 2015, the agency announced that they were melding their criminal and civil fingerprint databases. They also decided to make all files searchable for potential culprits.

Satellites DNA:

In Genetics, the satellites are repetitive DNA regions, located on telomeres and centromeres and abnormal repeats halt DNA replication. It clearly indicates that satellites help to do proper replication. Mutation in those sequences causes the end replication errors or problems.

Note one thing here, these satellite DNAs are non-coding.

Mainly two types of satellite regions are present in the human genome based on their repeat sequence nature: minisatellite and microsatellites .

Minisatellite region contains repeated DNA sequences of 10 to 60 bp. 5 to 50 repeats of it are present in our genome. For example, VNTRs.

minisatellites are highly variable (polymorphic), unique, and GC-rich sequences. As we said above, It is found mostly in telomeric regions (90% sequences).

Contrary, microsatellites are smaller than minisatellites. It’s 1-6 bp long and repeated 5 to 10 times in a genome. For example, STR and SSR. Read more on STR- short tandem repeats.

These regions are also hypervariable, non-coding and telomeric, likewise the VNTRs.

We have covered the entire article on VNTR and STR in genetic marker, for a more detailed understanding of genetic marker read the article: Genetic markers.

The first microsatellite was discovered by Jeffrey and his coworkers in 1984. Although, the name microsatellite was given by Litt and Luty in 1989.

An interesting story:

Everyone assumes that the name satellite is given because the sequences are located on the telomeric region of chromosomes but this conception is not true.

Because of their nature of separation in the centrifugation process, the name satellite DNA is given.

A larger portion of the human genome is made up of repeated sequences and hence it appears as a thick prominent layer on the top of the test tube after the centrifugation. So the name is given as a satellite DNA.

Now get back to our original topic,

Jeffreys and coworkers had identified the first microsatellite. The DNA fingerprinting was performed through RFLP & autoradiography by them.

Jeffrey had performed restriction digestion using REase and separated various DNA fragments using agarose gel electrophoresis. In the next step, the separated DNA fragments were transferred to a nylon sheet to perform southern hybridization. Radio-labeled probes were hybridized to detect various fragments.

The results were analyzed with the help of the X-ray film. This was the first method adopted by scientists to prepare a DNA fingerprint.

Before going further on different techniques of DNA fingerprinting, lets first understand the correlation between tandem repeats and DNA fingerprinting.

Some of the related articles,

The Different Methods Used

When first described in 1984 by British scientist Alec Jeffreys, the technique focused on sequences of DNA called mini-satellites that contained repeating patterns with no known function. These sequences are unique to each individual, with the exception of identical twins.

Different DNA fingerprinting methods exist, using either restriction fragment length polymorphism (RFLP), polymerase chain reaction (PCR), or both.

Each method targets different repeating polymorphic regions of DNA, including single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs). The odds of identifying an individual correctly depends on the number of repeating sequences tested and their size.

Some Remarkable Events in the DNA Fingerprinting History

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In the year 1935 Andrei Nikolaevitch Belozersky was able to isolate DNA in its pure form and in 1953 James Watson and Francis Crick explained double helical structure of DNA. Later in the year 1966, Marshall Nirenberg, Heinrich Mathaei, and Severo Ochoa demonstrated and explained about the genetic codes in the DNA which consisted of three nucleotide base each of 20 amino acids. These were among the most important events before the invention of DNA fingerprinting which have contributed a lot in finding a DNA profile. Following are some of the most important events in the DNA fingerprinting history.

✪ The history begins with the invention of this technique. Dr. Alec J. Jeffreys in 1984 found out that there is a repeating sequences in the DNA known as VNTRs (variable number of tandem repeats) which can be seen as the bar code in the X-ray pictures. These sequences were unique and even a small part of these codes was enough to determine the identity of an individual.

✪ Firstly DNA fingerprinting was used in the immigration case. It helped in finding out the relation between the immigrants with the people they claim as their close relatives. It was a great success and was a great event in the history of DNA profiling.

✪ In 1986, DNA fingerprinting was used in the criminal case for the first time. At that time, Richard Buckland was accused for the rape and murder of two young school girls. The DNA test was found negative when the semen sample collected from the two girls did not match with the accuse’s. He was the first person to be found innocent with the help of DNA fingerprinting.

✪ In 1987, Robert Melias who was accused of raping a 43 year old woman was found guilty when the semen stain on the woman’s clothes matched the DNA structure of the accused. This made him the first person to be found guilty with the help of DNA fingerprinting.

✪ There are many cases of fake DNA evidences and the first which came into picture was in 1992, when Dr. John Schneeberger raped a sedated patient and then planted semen on her underwear.

✪ In 1993, research team led by Daniel Cohen, of the Center for the Study of Human Polymorphisms in Paris, presented a report on all the 23 pairs of chromosomes found in the human body.

✪ In 1995, Perkin-Elmer developed a mapping kit with markers every 10 million bases along each chromosome. This added to the trustworthiness to the DNA fingerprinting techniques.

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

✪ In 1995, polymerase chain reaction (PCR) which is a techniques used in DNA fingerprinting, got acceptance in the court. It was from this time that the DNA fingerprinting was considered to be a reliable forensic evidence.

✪ In 1995, former football player O.J. Simpson was found not guilty for the murder of his ex-wife Nicole Brown Simpson and her friend Ronald Goldman. This was found out with the help of PCR and DNA fingerprinting and the player was released. This was one of the most famous controversial murder cases of that time.

✪ In 2000, the Attorney General of Ohio acknowledged DNA fingerprinting as “the most powerful crime-fighting tool we have at our disposal.” He said this in context with a case of sexual assaults which took place in New York.

✪ In 2001, DNA fingerprinting was used to find out the perpetrators and victims of World Trade Center attack which took place on 11th September. Identity of thousands of people was found out with the help of the remains of that disaster.

✪ Anna Anderson who was born somewhere in 1920s and died in the year 1984 claimed to be Russia’s Grand Duchess Anastasia, but later in the DNA fingerprinting it was reveled that her DNA does not matches with any of the living relatives of the Romanov royal Family.

✪ In 2007 it was found that United States holds the largest DNA database with the combined DNA index system of more than 5 million records.

Well, there is a huge list of events which took place in the history of DNA fingerprinting. Today DNA profiling is one of the major and trusted method in the forensic departments. Thousands of criminals have been caught and hundreds of innocent people have been released. Finding out hereditary diseases and other complications in an individual is also among the important DNA fingerprinting uses. So we can say that this is one of the most important inventions in the human history.

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PCR - DNA Fingerprinting

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Because DNA is unique to an individual, we can use DNA fingerprinting to match genetic information with the person it came from. First, we use the polymerase chain reaction (PCR) technique to copy a tiny fragment of DNA so that there is enough to use in gel electrophoresis. Gel electrophoresis uses gel and electricity to separate DNA fragments based on size, creating a distinct pattern that represents an individuals genetic information.

In shows like CSI, Miami, New York or wherever they often throw up the term DNA fingerprinting. One of the most common methods of DNA fingerprinting is something called PCR and what it's all about is using PCR and Gel Electrophoresis to examine DNA that's what they mean by DNA fingerprinting it's not really somebody's finger print. Now PCR stands for Polymerase Chain Reaction which is a process for copying DNA and what it does is that it uses a special heat stable DNA Polymerase to copy a specific gene that you're interested in.

Now Gel Electrophoresis is this idea of using the fact that DNA is negatively charged to take your copy DNA put it into the agarose gel or some other materials and then you use electricity to drive that charged DNA through the gel and because that gel acts like an obstacle force it separates up the DNA fragments based on their size. Let's take a closer look at this YouTube video that shows the process known as PCR and we're inside of a test-tube filled with DNA from suspect if we're in CSI but all we're interested in, is this one particular section of DNA called the target sequence highlighted in green. Now this is going to take advantage of some of the steps involved in DNA replication the process of copying DNA.

Now normally with DNA replication we have to open up the helix, well to open that up in your cells you use an enzyme. In this test tube we're going to heat it up to 95 degrees Celsius which will separate the two sides, because that is almost boiling temperature. Now we cool it a little bit and allow a premade thing called a primer that tells which gene we're interested in copying to come in and so by cooling to right around 60 odd degrees or so that allows the primer to bind to our target sequence. Now the orange little things is that enzyme that can survive these high temperatures. And these green guys with sticks on them, those are the nucleotides the raw material for building our DNA copy. So the enzyme does what it's supposed to do, it finds the primer and says okay and it starts copying, and it keeps going.

And if you give it enough time it'll finish copying the entire molecule going this way and that one will copy going that way. Remember the two strands of DNA are anti-parallel, they go on opposite directions. But we only give it maybe 2 minutes at most and so at that point we then let it stop and we're at the end of cycle one. And so now that we're done with cycle one we can begin cycle two and it's the exact same thing, we heat it up to 95 degrees Celsius which is enough to separate our old, original template strands and our newly made copies. We cool it to 60 degrees Celsius that's cool enough for the primers that still are floating around in the test tube to bind to the beginning and end portions of our gene of interest. Then we go to the right temperature for the enzyme, the DNA polymerase it finds the primer and goes okay and it starts to copy and that's the end of cycle two.

At this point we have 4 copies now each of our copies contains information that's not part of our DNA but at the beginning of cycle 3 when we heat it up notice there's a couple of short little segments that are only the length of our gene of interest. We cool it, primer stick, the tag-primers comes along and binds it, it's called tag-primers that's short for thermokineses which is just the name of the creature came from but now we have a couple of our target molecules made. So we're ready to begin I believe this is cycle 4, so again we're going to heat it up, that' the end of cycle 3 so we heat it up for cycle 4, we separate our strands, we cool it enough for the primers to come on in, they bind to the beginning and end portions of our DNA gene tag polymerase does it's copying job and again we've made a number of copies of just the size that we want. Now original we had more of these longer ones but now we're starting to get more and more of the shorter ones.

As we begin cycle 5 we do the exact same thing over and over that's why it's called a chain reaction, each time we're doubling the number of our copies. And we just run it through, and this is such a simple process, this is one of the reasons why this when it was first invented people were going wow how did they think of this and there's a lot of a pack full of stories about how the guy actually did think of that, but he is niow a very rich man because everybody does this process. Now you can see we've got 22 molecules and that's after only 5 cycles. Each cycle takes maybe 90 seconds to couple of minutes, so you this 30 times and that takes you maybe 90 minutes and at the end of it you've got a large number, billions of copies of your target.

Now you can't see an individual molecule but you can see billions of molecules. Now how are we going to visualize this? How are we going to see how big that is? That's where the Gel Electrophoresis comes in. So we'll stop the YouTube and we'll go to a PowerPoint slide and let's imagine we've done a DNA fingerprint of 3 people and we're looking to see, we're not using this to identify who they are like you would see a side, but we're doing this trying to figure out what genes do they have? Let's suppose we've found a gene that if you have a longer version of it, you're more likely to get a particular cancer. If you have a short version of it, you're less likely to get a particular cancer.

Well we have patient 1, patient 2 and patient 3, now in this fourth row here what we have is pre made DNA so that we can use it like a ruler and what we do is we loaded our DNA samples into these holes here called the wells. We turn on the current, this end is negatively charged, this end is positively charged DNA has a negative charge to it so it is repelled by the negative side and goes zoom towards the positive end. And little guys one thousand base pairs long move a lot faster than the big 10,000 base pair of long pieces of DNA. Now this person here, we only see one band, this person here we see one band, this person we see two. Why is that? Oh yeah everybody has two copies of every gene, this person has two copies of the long version. Their homozygous for this particular condition.

What is DNA Fingerprinting? (with pictures)

DNA fingerprinting is a way of identifying a specific individual, rather than simply identifying a species or some particular trait. It is also known as genetic fingerprinting or DNA profiling. As a technology, it has been around since at least 1985, when it was announced by its inventor, Sir Alec Jeffreys. DNA fingerprinting is currently used both for identifying paternity or maternity and for identifying criminals or victims. There is discussion of using DNA fingerprinting as a sort of personal identifier as well, although the viability of this is debatable.

The vast majority of a human's DNA will match exactly that of any other human, making distinguishing between two people rather difficult. DNA fingerprinting uses a specific type of DNA sequence, known as a microsatellite, to make identification much easier. Microsatellites are short pieces of DNA which repeat many times in a given person's DNA. In a given area, microsatellites tend to be highly variable, making them ideal for DNA fingerprinting. By comparing a number of microsatellites in a given area, one can identify a person relatively easily.

The sections of DNA used in DNA fingerprinting, although highly variable, are passed down from parents to their children. Although not all of the sections will necessarily be passed on, no child has pairs that their parents do not have. This means that by comparing large groups of these sections, paternity, maternity, or even both, may be determined. DNA fingerprinting has a high success rate and a very low false-positive rate, making it an extremely popular form of paternity and maternity verification.

In forensics, DNA fingerprinting is very attractive because it doesn't require actual fingerprints, which may or may not be left behind, and may or may not be obscured. Because all of the DNA sections are contained in every cell, any piece of a person's body, from a strand of hair to a skin follicle to a drop of blood, may be used to identify them using DNA fingerprinting. This is useful in the case of identifying a criminal, because even a drop of blood or skin left at the crime scene may be enough to establish innocence or guilt, and it is virtually impossible to remove all physical trace of one's presence. DNA fingerprinting is useful in the case of identifying victims because even in cases where the body may be disfigured past identification, and teeth or other identifying features may be destroyed, all it takes is a single cell for positive identification.

DNA fingerprinting is by no means perfect, however. It cannot establish beyond the shadow of a doubt that a specific cell comes from a specific person it can only establish a probability. In many cases this probability is very high -- one in ten billion, for example -- but in some cases it may be much lower. The probability also becomes obscured when dealing with direct descendents, who may share a large portion of the examined areas of DNA with a parent.

Despite these problems, DNA fingerprinting is becoming more and more prevalent in the world of criminal forensics. Though some legal questions exist, such as the conclusiveness of DNA fingerprinting and the extent to which it is legal by national laws to compile databases of people's DNA and to take samples of their DNA for comparison, the benefits currently seem to outweigh the problems.

How unique are fingerprints, really?

Has anybody ever actually worked out the math on this? How many possible configurations and arrangements of loops and whorls could there actually be?

EDIT: To make this a bit more of a manageable problem, let's assume we're using current levels of fingerprint analysis used for prosecution of crimes.

Fingerprints isn't just about loops, arches and whorls - those are just overall patterns. A full fingerprint analysis involves noting the location of each minutiae - the ridge endings, bifurcations, deltas, and even pore locations. It is their relative location to each other that is used to individualize prints.

When asking what the number of possibilities there are, that's really based on the method by which you resolve the details. The question is like asking how many types of rectangles there could be in a 1 m by 1 m matrix - if I'm recording pixels that are 1 cm big, rectangles that differ by, say, 1 mm, would look identical. Of course, it isn't just spatial relationship that matters here, as skin is a deformable substrate, so the same finger can leave different prints. The idea is the same though - unlike DNA, where the basis are discrete units, probabilities based on three-dimensional relations are difficult to quantify.

A good example being the coastline paradox.

I think the question isn't how unique a fingerprint is at a moment in time. The question is how unique a stable fingerprint is over longer periods.

Any biometric is nearly infinitely unique at the moment of capture. Agreed, that problem is like "how many points can you fit in a rectangle."

The useful property is the envelope containing the feature over a period of 1, 5, 10 years. That envelope pulls us into things of finite complexity, and you start to get collisions between different people's biometrics once you discard attributes that can't be re-measured with consistency.

The National Academy of Sciences issued a report a few years ago that highlighted serious flaws with forensic sciences (including fingerprints). As part of that report the NAS found that there is no real scientific evidence calculating how unique a fingerprint is - instead it is a presumption that many professionals have made because "it has always been that way."

The comparison is between fingerprint uniqueness and DNA analysis, where for DNA an expert can determine with mathematical models and statistics how unique a sample of DNA is while a fingerprint sample can be analyzed by an "expert" and they cannot present any scientific or mathematical modeling to show how unique such a fingerprint actually is within the general population.

Source: I am a defense attorney that has done work on challenging forensic evidence with the NAS report and also:

Edit from one of the sources for a quick summary: "There is some evidence that fingerprints are unique to each person, and it is plausible that careful analysis could accurately discern whether two prints have a common source, the report says. However, claims that these analyses have zero-error rates are not plausible uniqueness does not guarantee that two individuals' prints are always sufficiently different that they could not be confused, for example. Studies should accumulate data on how much a person's fingerprints vary from impression to impression, as well as the degree to which fingerprints vary across a population. With this kind of research, examiners could begin to attach confidence limits to conclusions about whether a print is linked to a particular person."

Watch the video: DNA Fingerprinting. Genetics. Biology. FuseSchool (May 2022).