Explainer: DNA and DNA Profiling

Among various possible biometric modalities, DNA provides the most reliable personal identification. It is intrinsically digital, and does not change during a person’s life or at the time of their death.

Deoxyribonucleic acid is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses.

In the human body, DNA, which can be thought of as the blueprint of biological design, is folded inside the nucleus of each cell. It is estimated that the human body is composed of approximately 60 trillion cells.

DNA are nucleic acids. Alongside proteins, they compose the three major “macro-molecules” essential for all known forms of life.

DNA is a polymer, and is composed of nucleotide units that each has three parts: a base, a sugar, and a phosphate. The bases are adenine, guanine, cytosine and thymine, abbreviated A, G, C and T, respectively. These four letters represent the informational content in each nucleotide unit.

DNA also has a backbone made of alternating sugars (deoxyribose) and groups of andphosphate material (which is related to phosphoric acid), with the nucleobases (G, A, T, C) attached to the sugars.

DNA is well-suited for biological information storage, since the DNA backbone is resistant to cleavage and the double-stranded structure provides the molecule with a built-in duplicate of the encoded information.

Variations in the nucleotide sequence bring about biological diversity, not only among human beings but among all living creatures. Phosphate and sugar form the backbone structure of the DNA molecule. Within a cell, DNA exists in a double-stranded form, which can be visualized as two anti-parallel strands that spiral around each other in the form of a double helix.

DNA is an excellent biometric identifier because it unique to each individual.  Although 99.9 percent of human DNA sequences are the same in every person, enough of the DNA is different to distinguish one individual from another, unless they are monozygotic twins.

Biometrics use methods for unique recognition of humans based upon one or more intrinsic physical or behavioral traits.  DNA can be classified as one of humanity’s most intrinsic features.  As a result, DNA profiling is often used for criminal investigations.

The DNA profiling technique was first used in 1984 and devised by Alec Jeffreys at the University of Leicester in England.  The technique is now the basis of several national DNA databases used for criminal justice. Dr. Jeffreys’s profiling technique was made commercially available in 1987, when Imperial Chemical Industries (ICI) started a blood-testing center in England.

DNA profiling begins with a sample of an individual’s DNA (typically called a “reference sample”). The most desirable method of collecting a reference sample is the use of a buccal swab, a non-invasive collection of DNA cells from a person’s cheeck, which reduces the possibility of contamination.

When this is not available, other methods may be used to collect DNA, including: a sample of blood, saliva, semen, or other appropriate fluid or tissue from personal items such as a toothbrush or razor. Stored samples such as banked sperm or biopsy tissue can also be used. Samples obtained from biological relatives can also provide an indication of an individual’s profile, as can human remains which had been previously profiled.

A reference sample is then analyzed to create the individual’s DNA profile using one of a number of techniques, which include RFLP, PCR and STR analysis, as well as Y-chromosome and mitochondrial analysis, along with AmpFLP and DNA family relationship analysis.

The DNA profile is then compared against another sample to determine whether there is a genetic match.  Such profiling is often used to solve high-impact and high-profile crimes, such as murder and rape.  The technology has be popularized in the media, by highly-rated dramas such as the CSI: Crime Scene Investigation television franchise.

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