DNA testing is a technology which evolved in the early 1980s, and which has been used increasingly ever since, often in controversial circumstances. It has been used to convict criminals, to release innocent people convicted of being criminals when they were not, and for other far less significant reasons.
One of the most common uses for this type of testing is in determining the likelihood of someone being the parent of a child. In its pure form, testing based on human DNA is accurate, but there are many factors which can lead to samples being corrupted, and erroneous conclusions being drawn.
The discovery of DNA brought forth the possibility of a vast improvement in crime detection. Genetic material left at crime scenes could be matched with that of individuals stored in a genetic data bank. Because of the extreme rarity of each DNA profile, pure samples had the power to be accurate to the degree needed for criminal prosecution. The possibility of achieving a fairer and more accurate legal system extended to child maintenance and paternity suits, where hard evidence would often be available to determine the truth.
The DNA samples which are used in legitimate detection are as unique as the human fingerprint, and are created from a combination of the DNA of both parents. This is why the technique is so especially suited to determining the parentage of a child when that issue is in doubt. In criminal investigations, the technique is better used to exclude someone whose DNA does not match the profile found at the scene, as it is rarely possible to be 100% certain using samples obtained from crime scenes.
Nevertheless, the possibility for error usually falls within fractions of one percent, so when used in conjunction with other evidence it is often conclusive. The possibility for error increases vastly as samples deteriorate and degrade, which is why some of the attempts to solve criminal cases which are decades old have resulted in such controversy. There have also been issues with equipment being used to collect samples being contaminated, sometimes resulting in the DNA of an innocent person being spread across several crime scenes.
There are also inevitable civil liberty issues surrounding DNA testing, as law enforcement authorities seek to build up data banks of DNA to use in investigations. Opponents argue that people are unaware that they are depositing forensic evidence in public places, and that even if they were aware there would be nothing they could do to prevent this happening. There is, however, the consideration that everything you do in a public place can be seen and witnessed so privacy does not exist anyway. Whatever the arguments, there are several people already who have been released from long prison sentences for crimes they did not commit, because of DNA testing.