How Long Does DNA Last?
Dioxyribonucleic acid (DNA) testing is covered extensively in the mainstream media, since it is used to solve crimes like murders, for paternity testing especially for illegitimate children, in archaeology and other applications. The DNA of each individual is unique and can be used to identify the person. Since DNA is mentioned extensively while reporting crime detection and DNA testing is also becoming popular worldwide as people try to trace their family history, many people would like to find out how long does dna last. The answer is that DNA is a molecule, and its life depends on a number of factors.
Where You Can Find a Person’s DNA:
The DNA of a person can be derived from a number of sources like the hair, skin, connective tissue, saliva, blood, with saliva usually extensively used by DNA testing companies which provide DNA related services to the public. These sources of DNA will degrade rapidly when exposed to sunlight, heat and water and will decompose within a few weeks. On the other hand, DNA also can be derived from the bones and teeth of a person. So if the skeleton of a person is buried under the ground, and not exposed, the DNA can be extracted hundreds of years later, and is often used for identifying kings and historical figures.
Hence the DNA of a dead person whose body is left outdoors will be significantly degraded within a few weeks, since the body degrades. On the other hand, for bodies which are buried below the ground, the DNA can be extracted between one thousand years to ten thousand years later. For example the oldest sample of human DNA which is found in Spain is seven thousand years old. If the body or other living creature is frozen at low temperature the DNA can be preserved for tens of thousands of years. Some of the oldest samples of DNA from Greenland are found in the frozen ice and are more than 450 thousand years old.
It Comes Down to the Molecules.
Like other molecules, the DNA molecule has a number of bonds which make it unique. Researchers have found that the half life of the molecule, the time taken for half the bonds in the molecule to be broken will be 521 years under ideal conditions. The time taken for all the bonds of the DNA molecule to be broken is 6.8 million years. However, after 1.5 million years, the DNA bonds are likely to have degraded to such an extent, that they cannot be used for DNA testing purposes. It should be noted that though the DNA sample may be sealed and frozen, the ambient radiation around it will cause the decay of the DNA and the sample will decay.
Which DNA is Used?
Often for DNA testing, either the blood or saliva is used, since the mitochondria and nuclei of the white blood cells and the dead cells of the mouth contain DNA. It should be noted that the DNA derived from mitochondria only contains partial genetic information. However this usually adequate for matching the DNA. Since the mitochondria are more abundant, the possibility of obtaining mitochondria DNA are higher, especially in the case of crimes and archaeological research. When the bodies of historical figures are found, usually mitochondrial DNA is used for testing purposes.
One of the major problems faced while using DNA for identification and research purposes is that it may be contaminated. In case of decayed bodies, the DNA may be contaminated with bacterial and other DNA, making it difficult to identify accurately. There is also a possibility that the DNA may be contaminated in the lab where the testing is taking place. In cases where a person has undergone a blood transfusion, the blood donors DNA may remain in the body of the recipient for a period of more than one year in some cases, depending on the amount of blood which has been received.
It should be noted that the condition of the body is not a very accurate indicator of whether the DNA is preserved. Many of the Egyptian mummies are thousands of years old, the body is preserved, yet the DNA has been destroyed in most cases due to the heat. Hence to preserve DNA for testing purposes the sample should be preserved using chemicals which prevent the decay of the molecule. This is the more convenient way. Alternately the DNA sample can be frozen. So there is no definite answer on how long the DNA will last for a dead organism or person, it depends on where the dead body is kept and the weather conditions in the area