Why is every fingerprint unique

Is the genetic fingerprint always unmistakable?

Only identical twins have the same DNA profile.

Only identical twins have the same DNA profile. Only those who know all the genetic fingerprints around the globe know whether those of other people are really unique. Since that is not possible, statistical methods help, says Walther Parson from the Institute for Forensic Medicine at the Innsbruck Med-Uni.

It is better than a classic fingerprint, but is not intended to replace it: the genetic fingerprint, in which DNA, i.e. deoxyribonucleic acid, comes from different tissues. "In the event of a possible conviction, the judiciary should be able to rely on many methods in parallel," says forensic scientist Walther Parson.

If the police find DNA traces at a crime scene that could help clarify a case, they are sent to the Med-Unis forensic medicine institutes in Austria. There several repetitive DNA segments are used for the analysis. For each person they form a characteristic pattern that can be represented on the computer as a numerical code. “These profiles vary widely across the population,” says Parson.

However, there can be no 100 percent security. To do this, you have to know everyone's fingerprints. The scientists therefore use statistical methods to determine probabilities, which are very high due to the great variety: an average DNA profile is only found by chance in less than a billion people on average. Genetic fingerprints from relatives are similar, so DNA analyzes are also used for paternity tests.

The researchers keep developing the methods. Whereas in the past a blood stain of a visible size was needed for an examination, today traces that cannot be seen with the naked eye are sufficient. Parson and his team are working on completely new techniques: With what is known as high-throughput sequencing, even severely damaged DNA should be able to be analyzed. They also want to help solve the case of the Mexican students who were killed in 2014.

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("Die Presse", print edition, July 25, 2015)