Paternity testing is an analysis of DNA that every day appear more and more in the media and tabloids to try to find out who is or who is not the son of Julio Iglesias, but does anyone know how these tests work? We tell you.
Basis of the technique
The basis of this technique is based on the “short tandem repeat” (STRs) or microsatellites; these are certain fragments that are found throughout our genome that are repeated a certain number of times and that, depending on the number of times they are repeated, correspond to a determined allele.
For example, an imaginary microsatellite found on the chromosome 2 and having the structure ATCT, for allele 8, will be repeated 8 times; …ACCGC(ATCT)8TCAG…, and for allele 13 will be repeated 13 times… ACCGC(ATCT)13TCAG…
Well, each person carries 2 different alleles in their genome for that particular microsatellite, one inherited from the mother and one inherited from the father. When analysing the alleles, we analyse those of at least 6 microsatellites that are distributed throughout the genome and are collected in the different jurisdictions of each country. The first step is to distinguish the APOs (obligatory parental alleles) of the offspring and then compare them with those of the father.
In this case we want to check whether two siblings are or are not sons of their father; to do this we must first identify the APOs by obtaining them through comparison with their mother; any allele that cannot come from the mother, will come from the father and will therefore be an APO.
When comparing the APOs with the alleles of the father comes the first moment where we can exclude paternity; in the case that at least 3 STRs do not correspond with the allele they should, we can directly exclude them, as in the case of offspring 2.
To confirm the paternity of the putative father with Child 1 is done on the basis of the probability of finding those particular alleles in a particular population. For this purpose and using a database where the probabilities of each allele are collected, we can complete the formula.
Once we have calculated the paternity index for each STR (see how to calculate it at the end); we can calculate the combined paternity index which is the result of multiplying all the indices separately. If the result is greater than 100; the alleged father can be said to be the father by 99%, if greater than 1000 by 99.9% and so on.
Thus, we already have some basic notions of the method by which paternity is or is not excluded in real life 😉
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