What are forensic genetics? |

Forensic Science and DNA Analysis

Forensic scientists use genetics for two primary legal applications: identifying the source of a sample of blood, semen, or other tissue, and establishing the biological relationship between two people in paternity or other kinship lawsuits. Forensic scientists are frequently called upon to testify as expert witnesses in criminal trials. One of the most useful sources of inherited traits for forensic science purposes is blood. Such traits include blood type, proteins found in the plasma, and enzymes found in blood cells. The genes in people that determine such inherited traits have many different forms (alleles), and the specific combination of alleles for many of the inherited blood traits can be used to identify an individual. The number of useful blood group systems is small, however, which means that a number of individuals might have blood groups identical to those of the subject being tested.

The ultimate source of genetic information for identification of individuals is the DNA found in the chromosomes. Using a class of enzymes known as restriction enzymes, technicians can cut strands of DNA into segments, forming bands similar to a supermarket bar code that vary with individuals’ family lines. The pattern, termed a DNA “fingerprint” or profile, is inherited, as are the alleles for blood traits. DNA fingerprinting can be used to establish biological relationships (including paternity) with great reliability, because a child cannot have a variation that is not present in one of the parents. Because DNA is a relatively stable biological material and can be reliably tested in dried blood or semen even years after a crime has been committed, DNA fingerprinting has revolutionized the solution of criminal cases in which biological materials are the primary evidence. The likelihood of false matches ranges from one per million to one per billion. These numbers, however, do not include the possibility of mishandling of evidence, laboratory errors, or planting of evidence.

Criminal Cases Involving DNA Evidence

On November 6, 1987, serial rapist Tommy Lee Andrews became the first American ever convicted in a case involving DNA evidence. Samples of semen left at the crime scene by the rapist and blood taken from Andrews were sent to a New York laboratory for testing. Using the techniques of DNA fingerprinting, the laboratory isolated DNA from each sample, compared the patterns, and found a DNA match between the semen and the blood. Andrews was sentenced to twenty-two years in prison for rape, aggravated battery, and burglary.

The 1990–91 United States v. Yee
homicide trial in Cincinnati, Ohio, was the first major case that challenged the soundness of DNA testing methods. A homicide victim was shot in his car, but not all of the blood at the scene was determined to be from the victim. DNA analysis by the Federal Bureau of Investigation (FBI) showed a match between blood from the victim’s van and from the car of defendant Steven Yee. The defense claimed that the matching DNA data was ambiguous or inconsistent, citing what they claimed to be errors, omissions, lack of controls, and faulty analysis. However, after a fifteen-week hearing, the judge accepted the DNA testing as valid.

In 1994, former football star O. J. Simpson was arrested and charged with the murders of his ex-wife Nicole Brown and her friend, Ronald Goldman. Blood with DNA that matched Simpson’s was found at Brown’s home and blood spots in Simpson’s car contained DNA matching Brown’s, Goldman’s, and Simpson’s. Furthermore, blood at Simpson’s home contained DNA that matched Brown’s and Goldman’s. During Simpson's trial, for the most part, the defense admitted the accuracy of the DNA tests and did not scientifically challenge the results of the DNA fingerprinting. Instead, they argued that the biological evidence had been contaminated by shoddy laboratory work and that some evidence had even been planted; the jury found Simpson not guilty of the charges against him. In 1997, a jury in a civil trial unanimously found Simpson liable for wrongful death and battery, in part because the burden of proof was less onerous according to the “preponderance of evidence” test.

Notable Paternity Testing

In February 2007, former Playboy playmate Anna Nicole Smith died, leaving behind a five-month-old daughter and two men claiming to be the child’s father. Before her death, Smith had been ordered by the Los Angeles Superior Court to submit the child, Dannielynn, for paternity testing in response to a lawsuit by Larry Birkhead, who claimed to be the biological father, although Smith’s lawyer Howard K. Stern was listed as the father on the birth certificate. The legal wranglings moved from California to Florida to the Bahamas, where the child was born and residing; finally, a Bahamian judge appointed Dr. Michael Baird, laboratory director of the DNA Diagnostics Center (DDC) in Fairfield, Ohio, as the court’s DNA expert and ordered the paternity testing. In April 2007, the DDC results confirmed that Birkhead was the biological father, and he was subsequently awarded custody of the girl.

Other Applications

Forensic genetics professionals have also been called on in recent years to identify victims in situations with mass fatalities, most notably the 2004 Indian Ocean tsunami and the 2005 Atlantic Ocean hurricane Katrina. In addition to natural disasters, mass casualties may result from transportation accidents and terrorist attacks. Forensic genetics professionals are brought in to collect and process remains for DNA identity-testing; bone and teeth fragments are the most reliable sources of DNA, but soft tissue may be used as well. Laboratories then establish separate information management systems specifically for this type of forensic DNA analysis.

Impact

DNA evidence is used in thousands of criminal investigations and tens of thousands of paternity tests annually in the United States. In addition, forensic DNA testing has been used to free previously convicted and incarcerated individuals, with an average sentence served of twelve years. The Innocence Project, a nonprofit organization founded in 1992 by Barry Scheck and Peter Neufeld, claims that as of June 2009, 240 wrongfully convicted people in thirty-three states and Washington, DC, have been exonerated through DNA testing. This includes seventeen people who were sentenced to death. However, in June 2009, the US Supreme Court ruled that an inmate has no automatic right to receive access to the DNA evidence used in his or her conviction for additional analysis at personal expense.

Databases containing DNA profiles of people already convicted of particular crimes are available to local, state, and national law enforcement officials; when investigating a crime, they are now able to test DNA collected at the scene to see if it matches that of anyone in the database. The Combined DNA Index System (CODIS) is one such database. It contains DNA profiles from convicted individuals, evidence collected in unsolved crimes, and missing persons. Such information may link serial crimes to each other as well as past unsolved cases to present ones. In addition, investigators may reopen cold cases using methods for testing DNA evidence that were not available at the time of the crime.

Key Terms




alleles


:

alternative versions of genes at a genetic locus that determine an individual’s traits





DNA fingerprinting


:

a DNA test used by forensic scientists to aid in the identification of criminals or to resolve paternity disputes





forensic science


:

the application of scientific knowledge to analyze evidence used in civil and criminal law, especially in court proceedings




kinship

:

genetic relatedness between persons





paternity testing


:

determination of a child’s biological father





Bibliography

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