A DNA test isn't something you do every day, so reading the results isn't easy at first glance .
Here in this article, we offer you the basic tools to help you discover what your DNA can tell you.
Note : Be aware that the interpretation of results explained in this article works for the following set of relationship tests :
- Paternity Test
- Maternity test
- Sibling Test
- Avuncular test
- Grandparents test
- Y Chromosome Test
- Test of Chromosome X
- Twin test
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 characterized by both his position on the DNA molecule, but also by its composition .
The invariable position of the gene on the chromosome is called the locus (or Loci). Since it is easily detectable due to its known location, the gene is often used as a reference genetic marker .
The composition of the gene , on the other hand, is often variable, because there is a different version 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.
Therefore, although two humans have a large majority of their genetic heritage identical, a certain set of sequences in their DNA remains specific to each individual . Thus, within the same species, there are a multitude of possible combinations.
Doing a DNA relationship test is in practice the making of a genetic profile or genetic fingerprint, making it possible to identify a person by the specificity of their 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 to read the results of a DNA test?
The results are sent in the form of a table like the example below:
The set of all values in the table constitutes the genetic profile . Knowing the structure of DNA and its mode of transmission between individuals allows us to obtain increasingly precise results.
The combined relationship index is given for each locus and determines a frequency percentage based on the matching allele found
The index is then expressed with the conclusion of the results for all the loci in a mathematical formula in base of 1.
- If the relationship index is greater than 1 :
So there is a good chance that the people tested are biologically related.
- If, on the other hand, the relationship index is less than 1 :
So there is a good chance that the people tested do not have enough genes in common to determine a biological relationship.
Watch out!! Some laboratories calculate the relationship index on a base of 10 and not a base of 1. But the calculation logic remains completely the same.
The index is often then translated into a percentage for a simpler understanding for the participants.
- A relationship percentage greater than 90% :
In the majority of cases 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, thus the biological relationship between the participants is discarded.
- It is possible during indirect relationship tests that your relationship percentage is between 10% and 90% .
In this case, the test cannot definitively answer your question regarding 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 is about mixed biological relationships within the same family , it will be very difficult to define a clear and precise result. The doubt will always be present, because DNA tests can bring inconclusive results .
In this case, please share all the information about your situation with the laboratory before ordering to be sure that you have the possibility of having a test that will answer your question.
How reliable is a DNA test?
The reliability of the results of a DNA test will depend on several factors:
1. Laboratory accreditation
Accreditation of a laboratory is a crucial factor in ensuring the quality and reliability of DNA test results. By checking the accreditation of a laboratory, you can ensure that the analysis methods used to search for a filiation link are reliable and conform to international standards.
This accreditation is obtained after a thorough evaluation of the process by an independent external committee.
The laboratory accreditation also ensures that the genetic analyses performed are legal and legally accepted. It is therefore important to check the laboratory accreditation before ordering a DNA test to maximize the reliability of the results.
By choosing an accredited laboratory, you can feel confident in the results obtained.
2. The declaration of your situation
It is important to clearly communicate your family situation, doubts, and potential relationships between participants before ordering a DNA test. The outcome of the DNA test will depend on this declaration, as it is linked to a possibility assessment. It is crucial to provide all relevant information to ensure accurate results.
3. The type of test
It is important to consider the type of DNA test before ordering it, as different tests offer varying degrees of reliability. Depending on the family situation, some methods of analysis will be more appropriate than others and can provide more accurate results.
In general, it is always recommended to carry out DNA tests directly with the concerned person, which maximizes the accuracy of the results obtained. It is therefore important to take the time to understand the differences between different types of DNA tests in order to make the best choice for you.
4. Type of sample
The sample type used for a DNA test does not impact the results, but some tests can only be done with a certain type of sample.
Although the reliability of the results is not directly affected by the sample type, it is important to choose a sample that provides enough genetic information to obtain reliable results. Not all samples reliably provide enough genetic information for a DNA test.
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 with no biological link within the same population .
Thus the tests are always made in comparison with the profile of an unrelated and randomly chosen individual in the ethnic population of the participants. All this in order to guarantee the chances of comparison on rarer alleles and thus improve the precision of the results .
Understanding the Relationship Index
DNA Test Result
What is DNA?
DNA is a long ladder-shaped molecule or double helix structure found in the cells of all living organisms. This molecule contains all the genetic information common to a species, also called a genome.
DNA thus has the instructions for how to grow, move, digest, heal or reproduce. These are the genetic instructions used in the evolution and functioning of all living organisms is also responsible for hereditary transmission .
In humans, the DNA in our cells rolls up and condenses into a ball to create what are called chromosomes. In total, we have 46 DNA molecule chromosomes in each nucleus of every cell in our body.
If we unwind the molecule, we see that DNA is made up of distinct and separable bits of information called genes.
How does heredity work?
Heredity is a genetic mechanism that allows the transmission within a species of physical and behavioral characteristics from one generation to the next .
Genetic information is transmitted during cell multiplication which begins with the egg cell (cell from which an individual originates) and continues throughout the life of the being.
This transmission of DNA from the parents takes place through the sexual cells (ovum and sperm) during fertilization. Each of the sex cells is made up of chromosomes that 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 women, all cells have XX sex chromosomes, the transmission will necessarily be an X chromosome.
In men, the sex chromosomes of cells are XY, therefore some spermatozoa have an X chromosome, others a chromosome Y.
- If fertilization is 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 his cell's nucleus, 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 splits in two, each takes with it a complete version of DNA. A specialized protein rereads it so that only the correct information is accepted so that the DNA is correctly copied.
But no one is perfect and sometimes a correction error slips in and slightly modifies the genetic instructions, this is called a mutation.
The first column designates
STR or Locus genetic markers used for comparison
Each allele is represented by two digits. 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 is identical on both chromosomes
The number of alleles indicates how many times a specific DNA sequence repeats
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:
Indirect relationship tests
( Sibling Test , Avuncular , Grandparents )
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 due to random but common inheritance.
Likewise, it is not because the alleles are similar that they necessarily come from the parent in common.
It is therefore very important to include one of the known parents if possible 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 find those in common from the father.
The mother being 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 then very difficult to determine the exact relationship between the participants
A brother and a sister for example that do not have the same pairs of alleles does not mean that they do not share the same parents
We have seen that the child receives half of its chromosomes from its father and the other half from its mother. We then know that the genetic profiles of the participants will always have to match a part of its alleles in each of the DNA regions analysed.
In other words, for a positive result, at least one allele number on each locus line must be identical between the parent and the tested child. If some alleles do not match, the presumed father or mother is excluded from the relationship.
The same logic applies for the Y Chromosome test.