Blood Group & Filiation
Blood is a liquid tissue which, despite appearances, has various elements that differentiate it among individuals. This variability (or polymorphism) of the blood composition makes it impossible to mix blood during transfusion, for example between certain groups of people . People with the same characteristic are said to belong to the same blood group .
What is a Blood Group ?
A blood group is a classification based on the presence or absence of substances grouped into 2 systems : ABO ( A, B, AB or O ) and in Rhesus ( + or - ) . There are, however, around 30 other classification systems in humans, but these are two of the most important, both in medical practice and for their genetic interests.
The ABO system makes it possible to classify the different blood groups according to the presence or absence of A or B antigens on the surface of red blood cells by following this principle:
- For blood group A : Red blood cells have A antigens and B antibodies .
- For blood group B : Red blood cells have B antigens and A antibodies .
- For AB blood group : Red blood cells have A and B antigens and no antibodies .
- For blood group O : Red blood cells do not have antigens and antibodies A and B.
An antigen is a molecule present on the surface of a red blood cell which, recognized by antibodies or cells of the immune system of an organism, is capable of triggering an immune response in it.
The compatibility and incompatibility of blood thus depend on the ABO and Rhesus antigenic systems which compose it . In other words, during a blood transfusion, if the person does not have the antigen compatible with the donated blood, the latter will develop an immune reaction against the red blood cells possessing the antigen and destroy them.
It is therefore important to classify the possible exchanges according to the type of blood but also to the recipient or donor position :
For blood group A:
- It can receive from group A and group O
- He can give to group A and group AB
For blood group B:
- It can receive group B and group O
- He can give from group B and from group AB
For AB blood group:
- It can receive group A, B, AB and O - (universal receiver)
- He can give to group AB
For group O:
- It can receive group O only
- He can donate to group A, B, AB and O - (universal donor)
The principle remains the same for the rhesus of the D antigen:
- A negative rh can only give and receive negative
- A positive rh can only give and receive positive
Family relationship & Sanguine Group
The Rhesus system refers to put it simply, to a specific antigen which is denoted by the letter D. Despite the fact that there are many more, the D antigen being the most common, it may or may not be present on the red blood cell. The status of a person's Rhesus D is thus described by a positive or negative suffix after the ABO type .
- The presence of the D antigen corresponds to rhesus positive +
- The non-presence of the D antigen corresponds to rhesus negative -
In case of doubt about a family tie, it is natural to think that the verification blood group can be used to define a parentage link between a father and his children. It is a method accessible which already allows you a first approach on the possibilities of relation even if this comparison presents all the same limits.
In general, it is considered that blood groups are used to exclude a fatherhood, rather than to confirm it . The reliability and number of combinations does not allow to define a biological relationship with certainty, but by deduction you can be sure that the parentage link is simply not possible .
It is also possible that the mutations which operate during transmission mask the true blood group of the desired profile. Thus these mutations can distort any conclusion concerning the paternity of a person.
Please find underneath a painting resuming all the theoretically possible combinations of the ABO system that can help you in the search for filiation and paternity.
How to define paternity with blood groups ?
The use of the Rhesus system and of the D antigen is much less precise for a search for parentage. The possible verification can only be confirmed in a specific case, since:
- If one of the two parents has a positive rh . Then the child can receive either the positive or the negative
- But if both parents have negative rh. Then the child will necessarily receive the negative rh
The blood type is passed down inheritance, as is the color of the eyes or hair. It is an inheritance which depends on a specific combination according to the blood group of the parents with the following possibilities: AA, BB, AB, AO, BO, OO .
It is important to note that each person has 2 alleles corresponding to the creation of the blood group. But only one of its 2 alleles is replicated on the profile of the child during transmission.
- An allele from the paternal chromosome
- An allele from the maternal chromosome
The random combination of these alleles defines a child's new blood type.
During this association, there are genes which can be dominant, dominated (recessive) or codominant.
- In an association between AO and BO, the O gene will be surpassed by the A and B gene
- In an association between AB, the genes jointly participate in the determination of the group
In the example below, the mother carrying the AO alleles and the father of AB alleles, there are 4 possible combinations for children:
How to verify parentage with blood groups ?
Here is a representation of the whole possible combinations that exist with the ABO system of blood group transmission.
The DNA paternity test is still the only absolutely reliable method to determine the link of biological parentage.
When the paternity test result is positive, the accuracy and reliability is usually over 99.99% and when the test result is negative, the accuracy is 100%.
Unfortunately, it is not possible to predict any parentage link by using blood groups between members of the same family (apart from parentage: father and mother) . Indeed, the possibilities of combinations being too important, a comparison of the blood group between brother and sisters, uncle / aunt or cousins does not bring any proof on the family relation.