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The paternity test aims to determine the biological relationship between two people. In other words, it allows us to determine who is the biological father or mother of a child. An extension of this type of analysis is kinship testing, which allows us to determine other types of family relationship: siblings, grandparents, aunts, uncles, cousins, etc.

Paternity and kinship tests consist of an analysis of the DNA of each individual to obtain the so-called genetic profile or genetic fingerprint. By comparing the genetic profiles obtained from two individuals, the relationship between them can be determined.

Test de paternidad

How does a paternity test work?

We inherit half of our genetic material from our father and half from our mother. In our DNA we find coding regions, the genes, which account for only 2% of our entire genome, and non-coding regions. In these regions we find, among other things, sections full of repeats: short sequences of DNA bases that are always strung together in the same way. Paternity tests are based on the analysis of these repetitive regions of DNA.

Scientists refer to these repeats as short tandem repeats (STRs). STRs are made up of between two and seven DNA bases that can be repeated many times. The sequence “GATC”, for example, may appear eight times in one person, but fifteen times in another.

They are as individual as a fingerprint and allow people to be identified almost uniquely (with the exception of identical twins).

A paternity test is not a genetic test, because it provides little information about inherited genes. Instead, it determines the length of individual DNA segments, and in doing so reveals much about ancestry.

The analysis starts with the extraction of DNA from a sample (usually saliva). Because the amount of DNA obtained from these samples is very small, it is first necessary to amplify the DNA in order to be able to analyse it. To do this, scientists use the polymerase chain reaction (PCR): millions of copies of the STR sections can be produced in a few hours. The DNA copies are then bound to a fluorophore to make them visible in the next step.

Paternity test, how it works

STR segments differ in length and so do their PCR-generated copies. Therefore, the sample obtained after amplification is sent through a narrow mesh network in which the smaller copies move faster than the larger ones. In this so-called electrophoresis, the speed with which the DNA copies migrate can be used to infer their length.

In a paternity test, between 15 and 40 DNA markers are analysed. At the end of the analysis, scientists have a large number of measuring points, separately for the father, the child and sometimes also the mother. However, this is not enough, the crucial step in a paternity test is the statistical evaluation of the data with special programmes

What samples are needed for a paternity test?

All cells in the body contain DNA. Therefore, samples of blood, hair or saliva (containing the body’s own cells) are suitable for analysis.

For paternity testing, saliva samples are usually used, as blood is more difficult to obtain and hair cannot always be clearly assigned. A swab of the oral mucosa is sufficient to obtain the sample.

A paternity test requires at least two samples: one from the child and one from the possible father. Ideally, a sample from the mother should also be tested. The results make it possible to rule out paternity or classify it as highly probable.

How reliable is a paternity test?

Samples obtained from the child and the possible father are examined in the laboratory. In this way, paternity can be ruled out at 100% or established with a probability of 99.9%. A paternity test can only indicate probabilities, even if they are sometimes very high.

What types of paternity tests are there?

● Non-legally valid paternity test by genotyping of 16 nuclear STRs (father/son or mother/son)

● Legally valid paternity test by genotyping of 16 nuclear STRs in identified samples with chain of custody (father/son or mother/son)

En Genosalut disponemos realizamos la prueba de paternidad informativa, la prueba de paternidad con validez legal y huellas genéticas.

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What is a paternity test?
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