DNA Test Result

A DNA test is not something that you do every day, so it is normal that reading the results is not easy at first glance . In this article, we offer you the basic tools to help you understand what your DNA can tell you.

Note : note that the interpretation of the results explained in this post works for the following set of relationship tests:

- Paternity DNA test
- Maternity DNA test
- Sibling DNA test
- Avuncular DNA test
- Grandparents DNA test
- Y Chromosome DNA Test

What is DNA?

DNA is a long, ladder-like or double helix-shaped molecule found in the cells of all living organisms. This molecule contains all the genetic information common to a species which is also called a genome.

DNA thus has the instructions for use which indicates how to grow, move, digest, heal or reproduce. These are the genetic instructions used in the development and functioning of all living organisms which are also responsible for hereditary transmission .

In humans, the DNA present in our cells rolls up and condenses in the form of a ball to create what are called chromosomes. In total we have 46 DNA molecule chromosomes in every nucleus of every cell in our body. If we unwrap the molecule, we see that DNA is made up of a distinct and separable piece of information called genes.


A gene is a segment of DNA containing an inherited genetic instruction that predetermines a specific trait in the shape of a living organism. It is characterised both by its position on the DNA molecule and also by its composition .

The invariable position of the gene on the chromosome is called Locus (or Loci). Since it is easily detectable thanks to its known location, the gene is often used as a reference genetic marker .


The composition of the gene , when it comes to it, is often variable because there are different versions of the same gene with unique genetic instructions. This is called the allele and can be found in different places on the same chromosome and even on other chromosomes.

So although two humans have a large majority of their genetic makeup identical, a certain set of sequences in their DNA remains specific to each individual . Thus within the same species, there is a multitude of possible combinations.

In practice, performing a DNA relationship test is the production of a genetic profile or genetic imprint, making it possible to identify a person by the specificity of his alleles .

There are gene sequences whose genetic instructions are short, repetitive but above all very variable. During the analysis, they must be identified, then amplified so that they are "visible" in order to be able to identify them and compare them between individuals.

Today many laboratories therefore use these short sequences introduced under the name of STR (Short Tandem Repeats) which make it possible to establish genetic fingerprints.


In addition, a version of the same locus can have a frequency of occurrence of between 5 and 20% in all individuals. A single locus therefore does not make it possible to designate a specific individual. Laboratories use between 15 and 21 different loci to ensure more reliable results .

How does heredity work?

Heredity is a genetic mechanism which allows the transmission within a species of characteristics physical and behavioural from one generation to the next .

Genetic information is transmitted during cell multiplication which begins with the egg cell (cell at the origin of an individual) and will continue throughout the life of the being.

This transmission of DNA from parents takes place through sex cells (ovum and sperm) during fertilisation. Each of the sex cells is made up of chromosomes which will be transmitted randomly to the fetus . Thus he receives 46 chromosomes : 23 from his father and 23 from the mother .

Among the 23 chromosomes, there is what is called the sex chromosome which will define the sex of the fetus. In the mother all the cells have XX sex chromosomes, transmission will necessarily be an X chromosome. In men, the sex chromosomes of the cells are XY, some spermatozoa therefore have an X chromosome, others a Y chromosome.

- If the fertilisation is done with a carrier of the X chromosome, the child will be a girl .

- If it is with a carrier of a Y chromosome it will be a boy .


Then during cell multiplication, the information contained in the chromosome is transmitted from one cell to another and copied with the greatest care . The birth of a new DNA molecule begins when an unwinding protein separates the two strands of the double helix and undoes the rungs. In the fluid of the nucleus of its cell, the molecular letters of the genetic code float freely. Each strand of the helix copies its lost partner , resulting in two identical DNA molecules . This is how life reproduces genes and passes them on from one generation to the next.

When a living cell divides into two, each takes with it a complete version of DNA . A specialised protein reads it again so that only the correct information is accepted so that the DNA is correctly copied. But no one is perfect and it happens that a correction error slips in and slightly modifies the genetic instructions, this is what we call a mutation .

How to read the results?

The results are sent in the form of a table like the example below:

The first column represents

DNA regions, STR or Locus genetic markers used for the comparison

The allele number indicates how many times a specific DNA sequence is repeated


Each allele is represented by two numbers. This corresponds to the pair of chromosomes received, one by the mother and the other by the father

If there is only one number, it means that it is identical on both chromosomes

The set of all the values in the table constitutes the genetic profile . Knowledge of the structure of DNA and its mode of transmission between individuals allows us to obtain increasingly precise results.

The mother having 13 and 14 and the father 15 and 16, the child will then have 4 possible combination options:

In this kind of situation it is very difficult to correctly determine the relationship between the participants.

For example, a brother and a sister that do not have the same pairs of alleles, does not mean that they do not share the same parents.

The indirect relationship test is a test where statistics and probabilities play an important role in interpreting the results . Participants may have alleles that are different because of random yet common inheritance. Conversely, it is not because the alleles are similar that they necessarily come from the parent in common.

It is then very important to include if possible one of the known parents in order to greatly improve the accuracy of the results . Because the laboratory will therefore be able to set aside alleles from the mother, for example, to look for those in common from the father.

The combined index of relationship is given for each locus and determines a frequency percentage based on the corresponding allele found

The index is then expressed with the conclusion of the results for all the loci in a mathematical formula based on 1.

- If the relationship index is greater than 1 :

Then there is a good chance that the people tested are biologically related.

- If, on the other hand, the relation index is less than 1 :

Then there is a good chance that the people tested do not have enough genes in common to determine a biological relationship.

Attention !! Some laboratory calculates the relationship index on a base of 10 and not a base of 1. But the calculation logic remains quite the same.

The index is often then translated into a percentage for an easier understanding for participants.


- A relationship percentage greater than 90% :

In the majority of cases it is considered a positive test, thus the biological relationship between the participants is confirmed.


- A relationship percentage of less than 10% :

The test is considered negative, so the biological relationship between the participants is rejected.


- It is possible during the indirect relationship tests that your relationship percentage is between 10% and 90% .

In this case, the test cannot answer with certainty your question concerning the biological relationship between the participants.

It is recommended to avoid this kind of situation by involving the mother of the participant (s) to add genetic information to the test and thus improve the accuracy of the results .


- If your doubt relates to mixed biological relationships within the same family , it will be very difficult to define a clear and precise result. Doubt will always be present because DNA tests can bring inconclusive results .


In this case please communicate all the information concerning your situation to the laboratory before ordering to be sure that you have the possibility of doing a test which will answer your question.

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How reliable is a DNA test?

The reliability of the results during a DNA test will depend on several factors:

1. Laboratory accreditation  

Checking the laboratory's accreditation allows you to be sure of the analytical methods that scientists use when looking for a parentage link. An accreditation is an international standard that a laboratory can acquire after verification of the entire process by a  committee  external.

Accreditation gives the laboratory the possibility of genetic analyzes which may be legally legal.

2. The declaration of your situation  

Be sure to communicate well before your order on the family situation, your doubts and the possible relations between the participants. The result of the DNA test will depend on your declaration because it is linked to a deduction of possibilities.

3. The type of test

All DNA tests are not equal in terms of the odds ratio they offer, and depending on the basic situation several tests are possible and some more reliable than others.As a general rule, it is always advisable to do DNA testing directly with the affected person.  

4. The type of sample

The reliability of the results does not depend on the type of sample, but not all samples reliably provide enough genetic information to make a DNA test.

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We have seen that the child receives half of its chromosomes from its father and the other half from its mother . We know then that the genetic profiles of the participants will always have to coincide with a part of its alleles in each of the DNA regions analyzed.

That is, for a positive result, at least one allele number on each locus line must be the same between the parent and the child tested . If certain alleles do not match, the alleged father or mother is excluded from the relationship. The same goes for the Y Chromosome test.

Direct relationship tests ( Paternity Test ,  Maternity test & Y chromosome )

Indirect relationship tests are much more complex in interpretation for several reasons. Already such a complete genetic profile or it will never be able to define with certainty from which comes the inherited chromosomes. Indeed, the transmission of chromosomes is random from one individual to another and the possible combinations are multiple .

Take the example of a situation where we know the alleles of the mother and those of the father:

The indirect relationship tests (Brotherhood Test Avuncular, Grandparents)


The relationship index is a probability ratio which makes it possible to take into consideration that certain alleles are shared by a large number of individuals without biological links within the same population .

Thus the tests are always done in comparison with the profile of an unrelated individual and randomly chosen from the ethnic population of the participants. All this in order to guarantee the chances of comparison on rarer alleles and thus improve the accuracy of the results .

Understanding the relationship index