About DNA

Deoxyribonucleic acid (DNA) is often referred to as the molecule of heredity as it is responsible for the genetic propagation of most inherited traits. These traits can range from hair color to disease susceptibility.

During cell division, DNA is replicated and can be transmitted to offspring during reproduction. Lineage studies can be done based on the facts that the DNA in mitochondria (mitochondrial DNA) only comes from the mother, and the male "Y" chromosome only comes from the father.

Every person's DNA, their genome, is inherited from both parents. The mother's mitochondrial DNA together with twenty-three chromosomes from each parent combine to form the genome of a zygote (fertilized egg).

As a result, with certain exceptions such as red blood cells, most human cells contain 23 pairs of chromosomes, together with mitochondrial DNA inherited from the mother.

DNA in crime

Forensic scientists can use DNA located in blood, semen, skin, saliva, or hair left at the scene of a crime to identify a possible suspect, a process called genetic fingerprinting or DNA profiling.

In DNA profiling the relative lengths of sections of repetitive DNA, such as short tandem repeats and minisatellites, are compared.

DNA profiling was developed in 1984 by English geneticist Alec Jeffreys, and was first used to convict Colin Pitchfork in 1986 in the Enderby murders case in Leicestershire, England.

Many jurisdictions require convicts of certain types of crimes to provide a sample of DNA for inclusion in a computerized database.

This has helped investigators solve old cases where the perpetrator was unknown and only a DNA sample was obtained from the scene (particularly in rape cases between strangers).

This method is one of the most reliable techniques for identifying a criminal, but is not always perfect, for example if no DNA can be retrieved, or if the scene is contaminated with the DNA of several possible suspects.

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