Original DNA test: reliability and secrets of your genetic heritage

What if a simple DNA test was enough to shake up a family? In 2024, the film Cocorico brought together nearly two million spectators around the thorny question of origins. Beyond the laughs, the comedy raises a fundamental question: what does our genetic heritage really reveal?

Many foreign companies, mainly American, today promise individuals to determine the regions of origin of their ancestors from a simple DNA sample. In France, these so-called “recreational” tests are prohibited.

In France, only DNA tests carried out in a medical or judicial context, as well as those carried out within the framework of highly regulated scientific research, are authorized by law.

According to article 226-28-1 of the Penal Code, “the fact, for a person, of requesting the examination of their genetic characteristics or those of a third party, or the identification of a person by their genetic fingerprints outside the conditions provided for by law is punishable by fines of 3,750 euros. » Objective: to protect privacy. DNA is extremely intimate data, revealing not only information about origins, but also potential information about health and family ties.

Although in France, recreational DNA testing are prohibited and punishable by law, nearly 1.5 million French people have already used it. To order them, all it takes is a few clicks on the websites of companies – 23andMe, AncestryDNA or even MyHeritage, not to mention them – based abroad. You will then be given a kit to collect saliva DNA, usually using a swab rubbed against the inside of the cheek. A few weeks after returning the sample, the results will be communicated to you: they present an estimate of the geographical origins in the form of a map, as well as genetic matches with other users.

The price of the tests varies depending on the information desired: count around €90 to €100 for one. genealogical testand up to €200 with health data.

In comedy CocoricoFrédéric Bouvier-Sauvage, played by Christian Clavier, convinced that he comes from a line of French aristocrats, discovers to his amazement that he has 15% Cherokee origins. Do these “general public” tests provide truly reliable information on the origin of our ancestors? “ From a DNA sequencing perspective, these companies are using proven technologiesconfides Paul Verdu. However, unlike medical or basic research, which repeats analyzes to ensure the reliability of the results, these tests often rely on only a single analysis, in order to reduce costs. This results in a significant variability in data quality obtained. »

In general, close family ties are reliable because they are based on direct DNA matches.

On the other hand, the question of origins is much more thorny! The results of your DNA test suggest that you are 20% Irish-British, 19% Iberian and 35% French-German? This information should be taken with caution. “ The analyzes are based on complex calculations, the results of which vary depending on the assumptions made and the methods used.. However, the companies that market these genetic tests intended for the general public do not communicate about their methodology. This is an industrial secret, explains Paul Verdu. We cannot therefore, scientifically, judge their reliability. »

And to add: “ The results also mix several categories: countries (France), geographical areas (Western Europe). However, we cannot compare cabbages with carrots! These companies deliver “turnkey” results that are impossible to evaluate due to lack of access to the calculations, and the very way in which they are presented reveals great ambiguity. »