What is VNTR

Genetic fingerprint

English: genetic fingerprint

1 definition

The genetic fingerprint is a unique profile for each individual, which is created with the help of molecular markers and by means of which the person can be identified as by their fingerprint.

2 method

2.1 approach

These molecular markers are non-coding DNA segments made up of repeating units (tandem repeats) of special base sequences. Depending on how long such a unit is, these sections are called VNTR regions (Variable Number of Tandem Repeats) with 10-150 base pairs per unit or STR regions (Short Tandem Repeats) with a maximum of 7 base pairs per unit. Since mutations in the non-coding area have no direct consequences, there are particularly many here. The mutations lead to the fact that the number of repetitions of these special base sequences is very different from one individual to the next.

There are many loci in the genome with such repetitive units. The more of these loci are used for the analysis, the more clearly the result can be assigned to a specific person. With 8 loci, it is statistically true for only one person in the entire earth's population: the probability that the same pattern will arise in two unrelated people is 4x10-11, with relatives still at 4x10-5. The results would only be identical with identical twins, since they have the same genetic information - it is not possible to differentiate between them using the genetic fingerprint.

2.2 Implementation

The sequence of bases that frames such a locus is the same for all humans. This sequence can be recognized by restriction enzymes or primers so that the VNTRs / STRs can be specifically cut out or multiplied:

  • RFLP (restriction fragment length polymorphism): This method can be used if there is enough analysis material (at least 50,000 cell nuclei) and is done with the help of restriction enzymes. Restriction enzymes are enzymes that cut DNA according to special recognition sequences that are in front of and behind the locus. Depending on how many repetitions there are between these recognition sequences, DNA fragments of different lengths are created.
  • PCR: This method enables the analysis of even very small amounts of DNA and is preferred nowadays. By using special primers that recognize the base sequence at the beginning and end of the loci, the VNTRs / STRs can be specifically increased.

The DNA fragments obtained are then separated according to their size by means of gel electrophoresis and made visible, for example, by radioactively labeled gene probes.

The result is a special band pattern, similar to a barcode.

3 possible uses

These are extremely diverse:

  • Paternity test and relationship analysis: For this purpose, the genetic fingerprints of the respective people are compared with each other. The more similar the patterns are, the closer the relationship.

In the paternity test, the child's ties must be found with the parents, since the child combines half of the DNA of its mother and half of its father. If there are bands in the child that cannot be found in one of the parents, this indicates that the person tested is not the biological father.

  • Relationships in animals and plants can also be examined using the genetic fingerprint. Here, phylogenetic questions are usually in the foreground.
  • Medicine: Here, too, the possibilities are diverse, for example for genome mapping, in tumor biology or transplant medicine.
  • Forensic science: Here the genetic fingerprint is an important means of proving the perpetrator (traces at the crime scene can be clearly assigned to the perpetrator). Another possibility is the identification of burned corpses, for example.

In general, anything that contains nucleated cells can be used as analysis material, for example hair, traces of saliva, blood and sperm.

4 security

The error rate in examinations carried out from 1998 to 2002 was approx. 0.5%. The main sources of error were the mix-up of samples and errors when transferring the results.