The DNA of Relationships (Smalley Franchise Products)
Gary Smalley  More Info

Trace Your Roots with DNA: Use Your DNA to Complete Your Family Tree
Megan Smolenyak  More Info

Recombinant DNA: Genes and Genomics: A Short Course
James D. Watson  More Info

Unraveling DNA: Molecular Biology for the Laboratory
Michael R. Winfrey  More Info

Gene Cloning and DNA Analysis: An Introduction
Terry A. Brown  More Info

The Divine DNA: Your Identity With Divinity
Isaac Pitre  More Info

French DNA: Trouble in Purgatory
Paul Rabinow  More Info

The Double Helix: A Personal Account of the Discovery of the Structure of DNA
James D. Watson  More Info

Genes and DNA (Kingfisher Knowledge)
Richard Walker  More Info

DNA and Tradition: The Genetic Link to the Ancient Hebrews
Yaakov Kleiman  More Info

Sex, Drugs and DNA: Science's Taboos Confronted
Michael Stebbins  More Info

An Introduction to Forensic DNA Analysis, Second Edition
Norah Rudin  More Info

The Stuff of Life: A Graphic Guide to Genetics and DNA
Mark Schultz  More Info

Bones, Brains and DNA: The Human Genome and Human Evolution
Ian Tattersall  More Info

DNA & Genealogy
Colleen Fitzpatrick  More Info

James D. Watson  More Info

The DNA of Healing: A Five-Step Process for Total Wellness and Abundance
Margaret Ruby  More Info

Forensic Science


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Frequently Asked Questions about Forensic DNA


How does forensic identification work?

Any type of organism can be identified by examination of DNA sequences unique to that species. Identifying individuals within a species is less precise at this time, although when DNA sequencing technologies progress farther, direct comparison of very large DNA segments, and possibly even whole genomes, will become feasible and practical and will allow precise individual identification.

To identify individuals, forensic scientists scan 13 DNA regions that vary from person to person and use the data to create a DNA profile of that individual (sometimes called a DNA fingerprint). There is an extremely small chance that another person has the same DNA profile for a particular set of regions.

Some Examples of DNA Uses for Forensic Identification

  • Identify potential suspects whose DNA may match evidence left at crime scenes
  • Exonerate persons wrongly accused of crimes
  • Identify crime and catastrophe victims
  • Establish paternity and other family relationships
  • Identify endangered and protected species as an aid to wildlife officials (could be used for prosecuting poachers)
  • Detect bacteria and other organisms that may pollute air, water, soil, and food
  • Match organ donors with recipients in transplant programs
  • Determine pedigree for seed or livestock breeds
  • Authenticate consumables such as caviar and wine

Is DNA effective in identifying persons?
[answer provided by Daniel Drell of the U.S. DOE Human Genome Program]

DNA identification can be quite effective if used intelligently. Portions of the DNA sequence that vary the most among humans must be used; also, portions must be large enough to overcome the fact that human mating is not absolutely random.

Consider the scenario of a crime scene investigation . . .

Assume that type O blood is found at the crime scene. Type O occurs in about 45% of Americans. If investigators type only for ABO, then finding that the "suspect" in a crime is type O really doesn't reveal very much.

If, in addition to being type O, the suspect is a blond, and blond hair is found at the crime scene, then you now have two bits of evidence to suggest who really did it. However, there are a lot of Type O blonds out there.

If you find that the crime scene has footprints from a pair of Nike Air Jordans (with a distinctive tread design) and the suspect, in addition to being type O and blond, is also wearing Air Jordans with the same tread design, then you are much closer to linking the suspect with the crime scene.

In this way, by accumulating bits of linking evidence in a chain, where each bit by itself isn't very strong but the set of all of them together is very strong, you can argue that your suspect really is the right person.

With DNA, the same kind of thinking is used; you can look for matches (based on sequence or on numbers of small repeating units of DNA sequence) at a number of different locations on the person's genome; one or two (even three) aren't enough to be confident that the suspect is the right one, but four (sometimes five) are used and a match at all five is rare enough that you (or a prosecutor or a jury) can be very confident ("beyond a reasonable doubt") that the right person is accused.

How is DNA typing done?

Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next. Scientists can use these variable regions to generate a DNA profile of an individual, using samples from blood, bone, hair, and other body tissues and products.

In criminal cases, this generally involves obtaining samples from crime-scene evidence and a suspect, extracting the DNA, and analyzing it for the presence of a set of specific DNA regions (markers).

Scientists find the markers in a DNA sample by designing small pieces of DNA (probes) that will each seek out and bind to a complementary DNA sequence in the sample. A series of probes bound to a DNA sample creates a distinctive pattern for an individual. Forensic scientists compare these DNA profiles to determine whether the suspect's sample matches the evidence sample. A marker by itself usually is not unique to an individual; if, however, two DNA samples are alike at four or five regions, odds are great that the samples are from the same person.

If the sample profiles don't match, the person did not contribute the DNA at the crime scene.

If the patterns match, the suspect may have contributed the evidence sample. While there is a chance that someone else has the same DNA profile for a particular probe set, the odds are exceedingly slim. The question is, How small do the odds have to be when conviction of the guilty or acquittal of the innocent lies in the balance? Many judges consider this a matter for a jury to take into consideration along with other evidence in the case. Experts point out that using DNA forensic technology is far superior to eyewitness accounts, where the odds for correct identification are about 50:50.

The more probes used in DNA analysis, the greater the odds for a unique pattern and against a coincidental match, but each additional probe adds greatly to the time and expense of testing. Four to six probes are recommended. Testing with several more probes will become routine, observed John Hicks (Alabama State Department of Forensic Services). He predicted that, DNA chip technology (in which thousands of short DNA sequences are embedded in a tiny chip) will enable much more rapid, inexpensive analysis using many more probes, and raising the odds against coincidental matches.

What are some of the DNA technologies used in forensic investigations?

Restriction Fragment Length Polymorphism (RFLP)
RFLP is a technique for analyzing the variable lengths of DNA fragments that result from digesting a DNA sample with a special kind of enzyme. This enzyme, a restriction endonuclease, cuts DNA at a specific sequence pattern know as a restriction endonuclease recognition site. The presence or absence of certain recognition sites in a DNA sample generates variable lengths of DNA fragments, which are separated using gel electrophoresis. They are then hybridized with DNA probes that bind to a complementary DNA sequence in the sample.

RFLP is one of the original applications of DNA analysis to forensic investigation. With the development of newer, more efficient DNA-analysis techniques, RFLP is not used as much as it once was because it requires relatively large amounts of DNA. In addition, samples degraded by environmental factors, such as dirt or mold, do not work well with RFLP.

PCR Analysis
PCR (polymerase chain reaction) is used to make millions of exact copies of DNA from a biological sample. DNA amplification with PCR allows DNA analysis on biological samples as small as a few skin cells. With RFLP, DNA samples would have to be about the size of a quarter. The ability of PCR to amplify such tiny quantities of DNA enables even highly degraded samples to be analyzed. Great care, however, must be taken to prevent contamination with other biological materials during the identifying, collecting, and preserving of a sample.

STR Analysis
Short tandem repeat (STR) technology is used to evaluate specific regions (loci) within nuclear DNA. Variability in STR regions can be used to distinguish one DNA profile from another. The Federal Bureau of Investigation (FBI) uses a standard set of 13 specific STR regions for CODIS. CODIS is a software program that operates local, state, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and missing persons. The odds that two individuals will have the same 13-loci DNA profile is about one in one billion.

Mitochondrial DNA Analysis
Mitochondrial DNA analysis (mtDNA) can be used to examine the DNA from samples that cannot be analyzed by RFLP or STR. Nuclear DNA must be extracted from samples for use in RFLP, PCR, and STR; however, mtDNA analysis uses DNA extracted from another cellular organelle called a mitochondrion. While older biological samples that lack nucleated cellular material, such as hair, bones, and teeth, cannot be analyzed with STR and RFLP, they can be analyzed with mtDNA. In the investigation of cases that have gone unsolved for many years, mtDNA is extremely valuable.

All mothers have the same mitochondrial DNA as their daughters. This is because the mitochondria of each new embryo comes from the mother's egg cell. The father's sperm contributes only nuclear DNA. Comparing the mtDNA profile of unidentified remains with the profile of a potential maternal relative can be an important technique in missing person investigations.

Y-Chromosome Analysis
The Y chromosome is passed directly from father to son, so the analysis of genetic markers on the Y chromosome is especially useful for tracing relationships among males or for analyzing biological evidence involving multiple male contributors.

The answer to this question is based on information from Using DNA to Solve Cold Cases - A special report from the National Institute of Justice (July 2002).

Some Interesting Uses of DNA Forensic Identification

  • Kennewick Man
    Kennewick Man was discovered in the Pacific Northwest. His ancient remains have caused problems because of competing claims for the remains by Native American groups, public officials, and scientists. Bones found in the United States that predate the arrival of Europeans are by law considered Native American, but the bones of Kennewick Man show characteristics different from Native Americans of that time period. DNA testing will be used to determine if Kennewick Man's DNA is similar to that of other Native Americans.


  • Disappeared Children in Argentina
    Numerous people (known as "the Disappeared") were kidnapped and murdered in Argentina in the 1970s. Many were pregnant. Their children were taken at birth and, along with other young kidnapped children, were raised by their kidnappers. The grandparents of these children are now looking for them. Read an article about a DNA researcher who has been helping them.


  • Tomb of the Unknowns


  • The Murdered Nicholas Romanov, the Last Czar of Russia, and His Family


  • Son of Louis XVI and Marie Antionette
    PARIS, Apr 19, 2000 (Reuters) -- Scientists cracked one of the great mysteries of European history by using DNA tests to prove that the son of executed French King Louis XVI and Marie-Antoinette died in prison as a child. Royalists have argued for 205 years over whether Louis-Charles de France perished in 1795 in a grim Paris prison or managed to escape the clutches of the French Revolution. In December 1999, the presumed heart of the child king was removed from its resting place to enable scientists to compare its DNA make-up with samples from living and dead members of the royal family -- including a lock of his mother Marie-Antoinette's hair.


  • Peruvian Ice Maiden
    The Ice Maiden was a 12-to-14-year old girl sacrificed by Inca priests 500 years ago to satisfy the mountain gods of the Inca people. She was discovered in 1995 by climbers on Mt. Ampato in the Peruvian Andes. She is perhaps the best preserved mummy found in the Andes because she was in a frozen state. Analysis of the Ice Maiden's DNA offers a wonderful opportunity for understanding her genetic origin. If we could extract mitochondrial DNA from the Ice Maiden's tissue and successfully amplify and sequence it, then we could begin to trace her maternal line of descent and possibly locate past and present relatives.


  • African Lemba tribesmen
    In southern Africa, a people known as the Lemba heed the call of the shofar. They have believed for generations that they are Jews, direct descendants of the biblical patriarchs Abraham, Isaac, and Jacob. However unlikely the Lemba's claims may seem, modern science is finding a way to test them. The ever-growing understanding of human genetics is revealing connections between peoples that have never been seen before.


  • Super Bowl XXXIV footballs and 2000 Summer Olympic souvenirs
    The NFL used DNA technology to tag all of the Super Bowl XXXIV balls, ensuring their authenticity for years to come and helping to combat the growing epidemic of sports memorabilia fraud. The footballs were marked with an invisible, yet permanent, strand of synthetic DNA. The DNA strand is unique and is verifiable any time in the future using a specially calibrated laser.

    A section of human genetic code taken from several unnamed Australian athletes was added to ink used to mark all official goods everything from caps to socks from the 2000 Summer Olympic Games. The technology is used as a way to mark artwork or one-of-a-kind sports souvenirs.


  • Migration patterns
    Evolutionarily stable mitochondrial DNA and Y chromosomes have allowed bioanthropologists to begin to trace human migration patterns around the world and identify family lineages. An example:
  • Wine heritage
    Using DNA fingerprinting techniques akin to those used to solve crimes and settle paternity suits, scientists at the University of California, Davis, have discovered that 18 of the world's most renowned grapevine varieties, or cultivars, including varieties long grown in northeastern France such as Chardonnay, the "king of whites," and reds such as Pinot and Gamay noir, are close relatives.


  • DNA Banks for Endangered Animal Species


  • Poached Animals


  • Declining Grizzly Bear Population


  • Snowball the Cat
    A woman was murdered in Prince Edward Island, Canada. Her estranged husband was implicated because a snowy white cat hair was found in a jacket near the scene of the crime, and DNA fragments from the hair matched DNA fragments from Snowball, the cat belonging to the husband's parents. M. Menotti-Raymond et al., "Pet cat hair implicates murder suspect," Nature, 386: 774, 1997.


  • Angiosperm Witness for the Prosecution
    The first case in which a murderer was convicted on DNA evidence obtained from a plant was described in the PBS TV series, "Scientific American Frontiers." A young woman was murdered in Phoenix, Arizona, and a pager found at the scene of the crime led the police to a prime suspect. He admitted picking up the victim, but claimed she had robbed him of his wallet and pager. The forensic squad examined the suspect's pickup truck and collected pods later identified as the fruits of the palo verde tree (Cercidium spp.). One detective went back to the murder scene and found several Palo Verde trees, one of which showed damage that could have been caused by a vehicle. The detective's superior officer innocently suggested the possibility of linking the fruits and the tree by using DNA comparison, not realizing that this had never been done before. Several researchers were contacted before a geneticist at the University of Arizona in Tucson agreed to take on the case. Of course, it was crucial to establish evidence that would stand up in court on whether individual plants (especially Palo Verde trees) have unique patterns of DNA. A preliminary study on samples from different trees at the murder scene and elsewhere quickly established that each Palo Verde tree is unique in its DNA pattern. It was then a simple matter to link the pods from the suspect's truck to the damaged tree at the murder scene and obtain a conviction. [WNED-TV (PBS - Buffalo, N.Y.)]


DNA Forensics Databases

National DNA Databank: CODIS

The COmbined DNA Index System, CODIS, blends computer and DNA technologies into a tool for fighting violent crime. The current version of CODIS uses two indexes to generate investigative leads in crimes where biological evidence is recovered from the crime scene. The Convicted Offender index contains DNA profiles of individuals convicted of felony sex offenses (and other violent crimes). The Forensic index contains DNA profiles developed from crime scene evidence. All DNA profiles stored in CODIS are generated using STR (short tandem repeat) analysis.

CODIS utilizes computer software to automatically search its two indexes for matching DNA profiles. Law enforcement agencies at federal, state, and local levels take DNA from biological evidence (e.g., blood and saliva) gathered in crimes that have no suspect and compare it to the DNA in the profiles stored in the CODIS systems. If a match is made between a sample and a stored profile, CODIS can identify the perpetrator.

This technology is authorized by the DNA Identification Act of 1994. All 50 states have laws requiring that DNA profiles of certain offenders be sent to CODIS. As of January 2003, the database contained more than a million DNA profiles in its Convicted Offender Index and about 48,000 DNA profiles collected from crime scenes but which have not been connected to a particular offender.

As more offender DNA samples are collected and law enforcement becomes better trained and equipped to collect DNA samples at crime scenes, the backlog of samples awaitning testing throughout the criminal justice system has increased dramatically. In March 2003 President Bush proposed $1 billion in funding over 5 years to reduce the DNA testing backlog, build crime lab capacity, stimulate research and development, support training, protect the innocent, and identify missing persons. For more information, seethe U.S. Department of Justice's Advancing Justice Through DNA Technology.

More on CODIS

Ethical, Legal, and Social Concerns about DNA Databanking

The primary concern is privacy. DNA profiles are different from fingerprints, which are useful only for identification. DNA can provide insights into many intimate aspects of a person and their families including susceptibility to particular diseases, legitimacy of birth, and perhaps predispositions to certain behaviors and sexual orientation. This increases the potential for genetic discrimination by government, insurers, employers, schools, banks, and others.

Collected samples are stored, and many state laws do not require the destruction of a DNA record or sample after a conviction has been overturned. So there is a chance that a person's entire genome may be available --criminal or otherwise. Although the DNA used is considered "junk DNA" (STRs-single tandem repeated DNA bases), in the future this information may be found to reveal personal information such as susceptibilities to disease and certain behaviors.

Who is chosen for sampling is also a concern. In the United Kingdom, for example, all suspects can be forced to provide a DNA sample. Likewise, all arrestees --regardless of the degree of the charge and the possibility that they may not be convicted--can be compelled to comply. This empowers police officers, rather than judges and juries, to provide the state with intimate evidence that could lead to "investigative arrests." In the U.S., arresting people on less than probable cause just to obtain DNA evidence raises the question of Fourth Amendment violations against unreasonable search and seizure.

Practicality also is a concern. An enormous backlog of over half a million DNA samples waits to be entered into the CODIS system. The statute of limitations has expired in many cases where the evidence would have been useful for conviction .

Potential Benefits of DNA Databanking Arrestees
(According to Howard Safir, NYC Police Commissioner, 1999)

  • Most major crimes involve people who also have committed minor offenses.
  • Innocent people currently are incarcerated for crimes they did not commit; if samples had been taken at the time of arrest, these individuals would have been excluded early in the investigative process.
  • Moving the point of testing from conviction to arrest would result in savings in investigation, prosecution, and incarceration.
  • Investigators would be able to compare other cases against the arrested person's DNA profile, just as with fingerprints.

Mitochondrial DNA Explained

Every cell contains both nuclear and mitochondrial DNA. Nuclear DNA is found within the nucleus of the cell and is composed of two sources of DNA: the egg and the sperm. This type of DNA defines us as individuals and is most often used in forensic or paternity cases. The nuclear DNA of a forensic specimen from a crime scene is compared to a specimen from a suspect to see how similar they are. In terms of a paternity suit, the nuclear DNA of the child is compared to the nuclear DNA from the father to see if the father contributed to the child's DNA.

Mitochondrial DNA (mtDNA) is contained in the mitochondria of the cell. The mitochondria are organelles located outside the nucleus in the cytoplasm of the cell. These organelles are responsible for energy transfer and are basically the "powerhouses" of the cells. The CIL uses this form of DNA because it preserves well in bones and many of the casualties that we are attempting to identify do not have blood samples on file (unlike the modern military). This form of DNA is in short strands and therefore does not mutate or change form very quickly - it is relatively stable and can be compared across several generations. Mitochondrial DNA is only passed along the maternal line - so if we want to compare a sample from a casualty individual we have to obtain a blood sample from the mother or any of the siblings who would share the same sequence of mtDNA as the mother. If nieces or nephews were to contribute DNA samples, only the child of a sister would contain the proper sequence since a brother's child would obtain his or her mtDNA from his mother who would not be a blood relative of the deceased in question.

The chart below can help you determine whether you are an eligible mtDNA donor.

The number of eligible donors of blood (MtDNA) continues to decline, making these samples very important to future identifications. All maternal relatives of WWII, the Korean War, Cold War, and Vietnam War KIA (BNR) casualties are encouraged to contact the appropriate service and arrange blood (MtDNA) donation.

Contact the appropriate service casualty office (see number below).

Missing persons Branch 1-800-531-5501
Mortuary Affairs 1-800-531-5803

Casualty and Memorial Affairs Operations Center

Missing Person Section (POW-MIA Affairs)

Casualty Branch

U.S. State Department (for civilian unaccounted-for)

DNA Forensics Links

Combined DNA Index System
The Combined DNA Index System (CODIS) is the FBI's national databases of genetic identification codes. Each DNA sample is stored as a 13 digit number.

CODIS consists of two sub-databases. The forensic index contains DNA evidence found at crime scenes. The offender index contains the DNA profiles of known offenders of sex offenses and other violent crimes. CODIS is primarily a national database for DNA data accumulated at local and state levels. All 50 states participate. In order to decrease the number of irrelevant matches, the convicted offender database requires all 13 CODIS STRs to be present for a profile upload. Forensic unknown profiles only require 10 of the STRs to be present for an upload.

As of November 2005, 124,200 forensic profiles and 2.8 million offender profiles have been accumulated, making it the second largest DNA databank in the world behind the United Kingdom. As of the same date, CODIS has produced over 27,700 matches to requests, assisting in more than 29,600 investigations.

The CODIS server itself is hidden at an unknown location.

There are many privacy and ethical concerns accompanying CODIS. The foremost is that CODIS represents the holy grail of eugenics. The database could be interpreted to yield the criminal gene. Such a discovery would have tremendous potential for abuse. CODIS does not have such a capacity. First, it does not store actual genetic information- just short identification codes. Secondly, the identification codes are created from so called "junk DNA". This DNA is not believed to have any function or influence on human characteristics.

The growing public approval of DNA databases has seen the creation and expansion of many states' own DNA databanks. California currently maintains the third largest DNA databank in the world (naturally, as CODIS contains all states' databank information). Political measures such as California Proposition 69 (2004), which increased the scope of the databank, have already met with a significant increase in numbers of investigations aided.

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