A genetic fingerprint is a DNA profile of an individual that is highly characteristic of the individual . The DNA is obtained from cells that come from tissue or secretions such as sperm , skin cells or saliva . The process is also known as genetic fingerprinting or DNA fingerprinting in molecular biology . Alec Jeffreys came across the procedure by chance in 1984. In Germany it was first recognized as evidence in a criminal trial in 1988.
For the genetic fingerprint, between 8 and 15 sections from the DNA are currently reproduced using the PCR method. This method only examines non-coding areas of the DNA. These areas are called repetitive DNA and can be divided into highly repetitive and medium repetitive DNA .
While highly repetitive DNA is satellite DNA , medium repetitive DNA is subdivided again into the subgroups tandem repetitions (microsatellites e.g. dinucleotides and mini satellites e.g. VNTRs) and scattered retrotransposons (SINES e.g. Alu and LINES e.g. B. L1). The tandem repetitions mini satellites VNTR ( variable number of tandem repeats ) or STRs ( short tandem repeats ) are tandem-like repetitions of a certain sequence (repeats) that occur in the genome of all mammals , e.g. B. Repetition sequences such as ATATAT ... or TACTAC ... The number of repetitions is variable. This number is examined in the genetic fingerprint. Depending on the number of repetitions, the duplicated section has a certain length, which can be represented as a single band using gel electrophoresis in the agarose gel .
If a person is heterozygous at one gene location ( i.e. has an allele with ten repetitions and one with 15), then two bands of different lengths arise. It is not a matter of sequencing, but a pure fragment length analysis (similar to RFLP ).
The repetitive portion of the VNTRs is longer (10 to 150 base pairs) than that of the STR (2 to 7 base pairs). The entire tandem repeat is no longer than 100 to 15000 bp for VNTRs and 100 to 400 bp for STRs.
The probability that two individuals at a VNTR or a STR locus will have a different number of repeats is very high. If several of these regions are examined, a band profile is obtained that is represented with a certain frequency in the total population. A statistical statement can then be made about how many people have to be examined in order to randomly meet someone who has exactly this pattern. For the 8 to 15 VNTR systems examined above, this number is often in the range of several billion. The information obtained is converted into a mathematical model that can be processed digitally and thus compared automatically. The mathematical model is a pure aggregated number code.
In contrast to other DNA analyzes , in which genes from the coding regions of the DNA are examined by means of sequencing, which certainly allow conclusions to be drawn about possible diseases of the individual, the numerical code of the fragment length analysis allows almost no characteristics of the individual to be derived . However, the gender is determined via an additional locus. Certain abnormalities in the number of chromosomes, such as those underlying Down syndrome , are also disclosed.
Another method is RFLP : Here the DNA is cut with the help of restriction enzymes. These restriction enzymes recognize specific sections in DNA. Depending on how often such a section is present in a chromosome, the number and length of DNA fragments differ. These can then in turn be made visible by gel electrophoresis, etc.
Further methods are the DGGE or TGGE , the phospholipid analysis, the polymerase chain reaction (partly with DNA sequencing ), the RAPD , the STR analysis , the SSCP analysis or further developments of the RFLP such as AFLP , T-RFLP, ARISA, ARDRA .
Legal situation in Germany
In Germany, a genetic fingerprint against the will of the person concerned may only be taken if a court order. Two different approaches are possible here:
- The examination of trace material and body cells of the accused in the context of the investigation of a specific criminal offense ( StPO in conjunction with StPO).
- The DNA analysis for the purpose of establishing identity in future criminal proceedings ( StPO).
The judge may only order the latter investigation if the prerequisite for a criminal offense of considerable importance within the meaning of the Criminal Code is met, if the repetition of which a genetic fingerprint can be helpful to identify the perpetrator (in principle, a judicial order is also possible in the case of sedition or fraud ) .
The investigation is carried out if there is reason to believe that criminal proceedings will continue to be conducted against the accused in the future . For such a decision, the court must generally examine the individual case extensively and thoroughly and take into account the right to informational self-determination (Article 2 (1) of the Basic Law). This must also be evident from the justification. High demands are placed on the justification in particular if a prison sentence is suspended on probation at the same time because a favorable prognosis must be made for this suspension.
The cells for the genetic fingerprint may be removed after the examination has been ordered by a doctor (Section 81a (1) sentence 2 StPO).
In the case of criminal investigations, laboratories (usually state) are commissioned to filter out the parts that are important for identification from DNA samples and make them available to the BKA's DNA database , which then includes unknown DNA profiles (e.g. from crime scene traces or unknown corpses) compares stored DNA profiles of known people. The known profiles come from criminals from whom a biological sample was taken by swabbing the oral cavity (voluntarily) or by abrasion of the skin (if the person refuses to penetrate a body opening). In Germany, the commissioned laboratories do not receive any personal data for reasons of data protection law, samples (traces) only receive a clear identification. Through this separation, it is only possible for the investigating authorities to establish a causal connection between the results of the investigation and the persons. In the course of investigations, people can also be asked to voluntarily provide a genetic fingerprint in order to rule out suspicion of innocent people.
Legal comparison between classic and genetic fingerprints
A prerequisite for taking the classic fingerprint and the genetic fingerprint is the commission of a criminal offense under the StGB.
- The taking of a genetic fingerprint can only be permitted in the case of serious criminal offenses by means of a court order (Section 81g, Paragraph 1, No. 1 and 2, Paragraph 3, Clause 1 in conjunction with Section 81f, Paragraph 1, Sentence 1 of the Code of Criminal Procedure ).
- The classic fingerprint is taken by the police if they believe that it is a criminal offense and the fingerprint can be used as evidence in the course of the investigation.
Legal equation of the genetic with the classic fingerprint
In connection with the murder of the fashion designer Rudolph Moshammer , an expansion of the possible uses of the genetic fingerprint was discussed in Germany. A law proposal from several federal states , which was introduced to the Federal Council on February 18, 2005 , provided for, among other things, the lifting of the judge's reservation and the expansion of the catalog of criminal offenses.
Privacy advocates and civil rights organizations spoke out against the change in the law. The conference of the data protection officers of the federal and state governments considers the aim of the federal states to equate classic and genetic fingerprints as questionable.
The result of a DNA test, a fingerprint or any other trace alone cannot determine whether a suspect is guilty or not. Taken alone, a DNA profile only proves that a certain person has left traces in a place, on a person or on an object. Whether this happened during the crime can only be determined independently of DNA traces. For example, DNA traces could be secured ten years after a murder case ; they led to two suspects. One person claimed to have had a secret sexual relationship with the victim, while the person ultimately convicted denied having ever seen the victim.
Even if traces of DNA enable the investigation of crimes that occurred a long time ago, Martin Killias criticizes the fact that decades after the crime there is hardly any possibility of defending a defendant in an appropriate manner. On the one hand, innocent people and perpetrators with a lengthy, successful process of repression can just as credibly deny involvement in the crime, and on the other hand, it is very difficult to claim an alibi after decades or to check one.
Even with a hit rate of 99.999% in Europe, statistically speaking, more than 7,000 other people fulfill the analyzed DNA characteristic. The possibility that one of these other people could be the perpetrator must be ruled out by means of further evidence and circumstantial evidence.
The case of a 28-year-old worker who was innocently imprisoned for murder for six months became known as a false-positive result. The Berlin Humboldt Institute contaminated the samples during the analysis; the public prosecutor apologized in writing.
The error rate of regularly GEDNAP - collaborative study examined genetic fingerprints (STR) were, between 1998 and 2002 from 0.4 to 0.7%. The most common sources of error were mixing up samples and incorrectly transferring results. If the expected error rate when presenting the results of the genetic fingerprint in court is taken into account, this can significantly reduce the likelihood of a suspect being found guilty. Criminal procedural measures based on a DNA hit are regularly only allowed after a careful examination. Verification of the first sample by a second is mandatory.
The Heilbronn Phantom is an example of sources of error due to improper handling of samples and devices : Several very different crimes were wrongly assigned to the same perpetrator, as sampling sticks were contaminated with the DNA of an employee of the manufacturer.
In patients with a bone marrow transplant, blood tests usually reveal the donor's genetic fingerprint, and in rare cases a mixed chimera . In the case of an oral mucous membrane swab, there is usually a mixed chimera, while the original genetic information is retained in the hair roots.
Identical twins have identical DNA with the exception of the V (D) J regions in the T and B lymphocytes of the immune system . In the case of a “positive” result, the crime scene trace can therefore also come from the untested twin if the genetic fingerprint does not include the regions mentioned.
In March 2009, a pair of twins had to be released who are suspected of having broken into the department store of the West on January 25, 2009 and of having stolen millions worth of loot. The analysis of traces on a glove found at the crime scene showed a match with the DNA of both twins. Although it is certain that at least one of the two was at the scene, neither of the two could be proven to be involved in the crime, as the lead could come from the other.
- DNA analysis file of the BKA, National DNA Database
- Polymerase chain reaction
- DNA screening
- First murder cases resolved with genetic fingerprints:
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