DNA Test Results
- infotest ADN
- Dec 30, 2025
- 9 min read
DNA Test Results: How to Read and Interpret Your Results
You've carried out a DNA test and are about to receive your results? Reading a genetic report can seem complex at first glance, especially when it's your first experience. Rest assured, understanding DNA test results is accessible to everyone, provided you know a few basic concepts.
In this article, we offer you a comprehensive guide to help you decipher your genetic report. Whether you've performed a paternity test, siblingship test or any other filiation test, you'll discover here the keys to correctly interpreting your results and understanding what your DNA reveals about your biological links.
For which types of tests is this guide suitable?
The explanations presented in this article apply to all biological relationship tests, particularly:
Avuncular test (uncle/aunt and nephew/niece)
Each of these tests is based on comparative analysis of specific genetic markers, allowing a kinship link between participants to be established or excluded.
What is DNA? The basics for understanding your results
DNA, the genetic code of life
DNA, or deoxyribonucleic acid, is a long double helix-shaped molecule present in every cell of our body. This structure resembles a twisted ladder whose rungs contain all our genetic information.
In concrete terms, DNA constitutes the biological instruction manual that dictates the growth, functioning, reproduction and transmission of hereditary characteristics of all living beings. It's thanks to DNA that we inherit physical traits from our parents and in turn transmit them to our children.
From DNA to chromosomes: how our genetic heritage is organised
In our cells, DNA coils upon itself to form compact structures called chromosomes. Each human being possesses 46 chromosomes divided into 23 pairs within each cell. Half come from our mother, the other half from our father.
If we completely unravelled these chromosomes, we would discover that DNA is composed of distinct segments called genes. Each gene corresponds to a precise genetic instruction that determines a particular characteristic of our body.
Genes and their variants: locus and allele
A gene occupies a fixed position on a chromosome, a position we call a locus (plural: loci). It's precisely this stable location that allows laboratories to easily locate genes during genetic analysis. Genes therefore serve as reference genetic markers.
However, the same gene can exist in different versions called alleles. These variants contain slightly different genetic instructions, which explains why two individuals, whilst belonging to the same species, present unique characteristics.
Thus, even though all human beings share the majority of their genetic heritage, certain DNA sequences remain specific to each person. It's this specificity that allows an individual to be uniquely identified by their genetic fingerprint.
How does a relationship DNA test work?
The principle of genetic fingerprinting
Carrying out a relationship DNA test amounts to establishing a genetic profile or genetic fingerprint of a person. This fingerprint allows an individual to be reliably identified through the unique combination of their alleles.
Laboratories search for particular gene sequences called STR (Short Tandem Repeats). These short, repetitive sequences show great variability from one individual to another, making them ideal markers for differentiating people.
Why analyse multiple genetic markers?
A version of the same locus can appear in 5 to 20% of the general population. A single genetic marker is therefore not sufficient to identify a kinship link with certainty.
This is why accredited laboratories analyse between 15 and 21 different loci. The higher the number of markers studied, the more the results gain in precision and reliability. This multi-marker approach guarantees practically infallible genetic identification.
How does heredity work? The transmission of DNA from generation to generation
The mechanism of genetic heredity
Heredity designates the biological process by which physical and behavioural characteristics are transmitted from one generation to another within the same species.
Everything begins with the fertilised egg cell, resulting from fertilisation, which contains all the genetic information necessary for the development of a new individual. This information is then copied and transmitted to each new cell during cell multiplication throughout life.
Transmission through sex cells
Parents transmit their DNA to their child through sex cells: the ovum in women and the spermatozoon in men.
During fertilisation, the child inherits 23 chromosomes from their mother and 23 chromosomes from their father, for a total of 46 chromosomes. This transmission is random, which explains why two siblings can present marked physical differences despite having common parents.
The role of sex chromosomes
Among the 23 chromosomes transmitted by each parent, there exists a particular chromosome called a sex chromosome, which determines the biological sex of the child.
In women, all cells possess two X chromosomes. She therefore necessarily transmits an X chromosome to her child.
In men, cells possess one X chromosome and one Y chromosome. Some spermatozoa carry an X chromosome, others a Y chromosome.
Thus:
If fertilisation occurs with a spermatozoon carrying the X chromosome, the child will be a girl (XX).
If it's with a spermatozoon carrying the Y chromosome, the child will be a boy (XY).
DNA replication: copying genetic information
During cell multiplication, DNA must be copied with great precision so that each new cell has a complete version of the genetic heritage.
When a cell divides, a specialised protein unravels the double helix and separates the two DNA strands. Each strand then serves as a template to recreate its complementary strand, thus generating two identical DNA molecules.
Correction mechanisms verify that information is properly copied. However, occasionally an error slips into the process, creating a mutation. These mutations can slightly modify genetic instructions and contribute to genetic diversity.
How to read DNA test results?
The structure of the results report
Laboratories present DNA test results in table form, generally structured as follows:
First column: genetic markers
This column indicates the DNA regions analysed, that is the STR genetic markers or loci used for comparison between participants.
Following columns: alleles of each participant
For each genetic marker, you'll find the allele values of each person tested. Here's what you need to know:
Each allele is represented by one or two numbers. These numbers correspond to the chromosome pair received: one from the mother, the other from the father.
If only one number appears, this means both chromosomes carry the same allele.
The allele number indicates the number of repetitions of a specific DNA sequence on this locus.
The set of all values present in the table constitutes the complete genetic profile of each participant. It's by comparing these profiles that the laboratory can establish or exclude a filiation link.
Interpreting results from a direct relationship test
What is a direct relationship test?
Direct relationship tests primarily concern:
Paternity test
Maternity test
Y-chromosome test (paternal line)
These tests allow verification of a direct filiation link between a parent and child.
How to interpret the results?
As we've seen previously, a child inherits half their chromosomes from their father and the other half from their mother. Consequently, genetic profiles must necessarily correspond partially at the level of each genetic marker analysed.
Interpretation rule:
For a result to be positive, at least one allele number on each locus line must be identical between the presumed parent and the tested child.
If several alleles don't correspond, this means the presumed parent is excluded from biological parentage. The absence of concordance on several markers indicates with certainty that there is no direct biological link.
This logic also applies to the Y-chromosome test, which compares the paternal line between men from the same family.
Interpreting results from an indirect relationship test
What is an indirect relationship test?
Indirect relationship tests include:
Siblingship test (between brothers and sisters)
Avuncular test (uncle/aunt and nephew/niece)
Grandparentage test
These tests are more complex to interpret as they don't directly compare a parent to their child, but people sharing one or more common ancestors.
Why are these tests more complex?
Interpreting these tests presents several challenges:
1. Random heredity
Chromosome transmission is random. Two brothers or two sisters can inherit different chromosomes from their common parents. Thus, even whilst sharing the same biological parents, they can present different alleles on certain markers.
2. The impossibility of determining the exact origin of chromosomes
A genetic profile, however complete, never allows knowing with certainty from which parent each inherited chromosome originates. This uncertainty complicates the analysis of indirect kinship links.
Example:
Let's imagine we know the mother's and father's alleles:
The mother possesses alleles 13 and 14
The father possesses alleles 15 and 16
The child could therefore inherit one of the following combinations:
13 and 15
13 and 16
14 and 15
14 and 16
In a comparison between siblings, if one has inherited 13 and 15 whilst the other has inherited 14 and 16, their alleles won't correspond, even though they do indeed share the same biological parents.
The importance of a known parent's participation
To considerably improve the accuracy of indirect relationship test results, it's strongly recommended to include one of the known parents in the analysis.
By identifying alleles originating, for example, from the mother, the laboratory can isolate and compare only alleles inherited from the father. This method reduces uncertainty and allows much more reliable conclusions to be obtained.
Understanding the relationship index and percentages
What is the relationship index?
The relationship index is a probability ratio that takes into account the fact that certain alleles are shared by a large number of individuals without biological link within the same population.
To guarantee the reliability of analysis, laboratories always compare the genetic profiles of participants to that of an unrelated individual, chosen randomly from the corresponding ethnic population. This method allows rarer alleles to be favoured and increases the accuracy of results.
How is the relationship index calculated?
The relationship index is determined for each locus according to the frequency of appearance of the corresponding allele in the general population. A combined relationship index is then calculated by adding the indices of all loci analysed.
This index is generally expressed as a mathematical ratio based on 1.
Interpretation of the index:
Index greater than 1: there exists a strong probability that the tested people are biologically related.
Index less than 1: it's unlikely that the tested people share a biological kinship link.
Caution: Some laboratories calculate the index on a base of 10 rather than 1. The interpretation logic remains identical however.
Translation into percentage
To facilitate understanding of results, the relationship index is often converted into a probability percentage.
Positive result:
A percentage greater than 90% is generally considered a positive test. The biological relationship between participants is confirmed.
Negative result:
A percentage less than 10% indicates a negative test. The biological relationship between participants is excluded.
Inconclusive result:
If the percentage lies between 10% and 90%, the test doesn't allow a conclusion with certainty. This situation occurs primarily during indirect relationship tests.
In this latter case, it's strongly recommended to include the participation of the mother or another known parent to improve the accuracy of analysis and obtain a definitive result.
Particular situations: doubts about multiple biological relationships
If you have doubts concerning multiple biological relationships within the same family, it can be difficult to obtain a clear and definitive result. DNA tests can sometimes give inconclusive results in these complex configurations.
Our recommendation:
Before placing an order, we invite you to explain your situation in detail to the laboratory or our team. This approach allows determination of whether the envisaged test is suitable for your case and whether it will be able to answer your questions. Personalised support avoids disappointments and guarantees that you choose the most appropriate analysis solution.
What is the reliability of a DNA test?
The reliability of DNA test results depends on several essential factors that we detail below.
1. Laboratory accreditation
A laboratory's accreditation constitutes the primary guarantee of result quality and reliability. An accredited laboratory meets strict international standards and regularly submits to independent assessments to verify the conformity of its analysis procedures.
Why choose an accredited laboratory?
The analysis methods employed are proven and reliable.
Processes are standardised and controlled.
Results are legally recognised and accepted by relevant authorities.
You benefit from a guarantee of confidentiality and respect for ethical standards.
Before ordering a DNA test, always take time to verify the laboratory's accreditation. This simple precaution ensures results you can have confidence in.
2. Clear communication of your situation
The accuracy of your results also depends on the clarity of information you provide when ordering.
What should you communicate?
Your complete family situation
Your precise doubts and questions
Potential relationships between different participants
The laboratory relies on this information to correctly interpret results. A precise and honest declaration maximises the chances of obtaining a reliable and relevant answer to your questions.
Don't hesitate to explain your situation in detail, even if it seems complex to you. Laboratories are accustomed to dealing with varied family configurations and will know how to direct you towards the most suitable test.
3. The type of test chosen
Not all DNA tests present the same degree of reliability. As we've seen, direct relationship tests (paternity, maternity, Y-chromosome) offer superior precision to indirect relationship tests.
General rule:
It's always preferable to perform a direct test with the person concerned when this is possible. This approach maximises the reliability of conclusions.
Before ordering, find out about the different types of tests available and choose the one that best corresponds to your situation and needs.
4. The type of sample used
The type of sample used for a DNA test doesn't directly influence result quality. However, not all samples reliably provide a sufficient quantity of DNA.
Standard samples:
Buccal swabs (cheek swabs) constitute the reference sample. They allow DNA to be easily and effectively collected in sufficient quantity for complete analysis.
Non-standard samples:
Some tests may require the use of alternative samples (hair with root, dried blood, etc.). Whilst technically usable, these samples can sometimes contain less DNA, which may require additional laboratory treatments.
Our advice:
If you have doubts about a sample's viability, contact the laboratory before sending it. Experts will be able to advise you on the most suitable sample type for your situation and guarantee the best chances of analysis success.