When the baby is born, a drop of blood is drawn to find out the blood group and Rh factor that it has inherited from its parents . It is not so easy to decipher it because it is not determined according to the combination of groups that the parents have, so we will explain below in a simple way some genetic laws that will help us to know what type of blood group and Rh factor the baby can inherit .
Often, the baby’s blood group can be surprising since it does not correspond to either of its parents, but it will depend on the genetic information inherited from each of them, since each person has two alleles from their father and from his mother.
Blood groups
A blood group is a classification of the blood according to the characteristics present in the red blood cells and in the blood serum. The two most important classifications in humans are antigens (A, B, O) and the Rh factor .
There are some basic notions of genetics that we must know to better understand the inheritance of blood groups:
-
The gene that determines the blood group has three variants or alleles: A, B and O that give rise to four blood groups: A, B, O or AB .
-
Every human being inherits genes from the father and the mother, but each of them in turn has dominant and recessive genes . Each person has two alleles, coming from his father and his mother. That is, even if the blood group is A, B, O or AB, the person will have a combination of genes that can be AA, AO, AB, OO, BB and BO .
-
Genes A and B are dominant and gene 0 is recessive , for example:
- A person with group AB has one gene A and another B.
- A person with group A can be AA or A0, but the dominant gene A prevails.
- A person with group B may be BB or B0, but the dominant B gene prevails.
- A person with group 0 has both genes 0.
What blood group will the baby have?
With what has been explained above, we can see that the inheritance of the blood group is not as simple as knowing the groups of the parents.
Each parent will give their child one of their two alleles. The possible combinations between the four heritable alleles (two from the father and two from the mother) give us 16 possibilities, which will determine the inherited group . For example:
-
PARENT GROUP A :
- Mother Group A: son Group A or 0
- Group B mother: Group 0, A, B or AB child
- Group AB mother: Group A, B or AB child
- Mother Group 0: son Group A or 0
-
PARENT GROUP B :
- Mother Group A: son Group 0, A, B or AB
- Mother Group B: son Group B or 0
- Group AB mother: Group A, B or AB child
- Mother Group 0: son Group B or 0
-
PARENT GROUP AB :
- Mother Group A: son Group A, B or AB
- Group B mother: Group A, B or AB child
- Group AB mother: Group A, B or AB child
- Mother Group 0: son Group A or B
-
PARENT GROUP 0 :
- Mother Group A: son Group A or 0
- Mother Group B: son Group B or 0
- Group AB mother: Group A or B child
- Mother Group 0: son Group 0
Let us remember that one allele of the gene that determines the blood group is inherited from the father and the other from the mother, but they, in turn, will be able to randomly transmit one of the two alleles that they have in their genetic makeup, which will be represented in the gamete, ovum and sperm. For this reason, the children of the same couple can have different blood groups , depending on the allele transmitted by each parent.
The combinations give rise to different examples of blood group inheritance depending on the way in which this inheritance occurs.
What Rh factor will the baby have?
In addition to blood groups, all people have a positive or negative Rh factor depending on the characteristics of their blood.
The Rh in the blood is determined by an antigen found on the surface of red blood cells or also known as red blood cells. These are the most common type of cells found in the blood and they are the main source for transporting the oxygen necessary for our body. We are Rh positive if the antigen is in our blood and Rh negative if we do not have it.
The inheritance of Rh is made up of two genes , one is inherited from the mother and the other from the father and follows a common pattern. The Rh positive gene is dominant , meaning that even when combined with an Rh negative gene, the positive one prevails. Therefore, the majority of people (85%) are Rh positive.
- If a person has the + + genes, the Rh factor in the baby’s blood will be positive .
- If a person has the + – genes, the Rh factor in the baby’s blood will be positive .
- If a person has the genes – – , the Rh factor in the baby’s blood will be negative .
Rh Factor inheritance:
-
MOTHER Rh- :
- Rh- father: Rh- son
- Rh + parent (++): Rh + child
- Rh + parent (+ -): Rh + or Rh- child
-
MOTHER Rh + (++) , in parentheses alleles inherited from parents:
- Rh- parent: Rh + or Rh- child
- Rh + parent (++): Rh + child
- Rh + parent (+ -): Rh + or Rh- child
-
MOTHER Rh + (+ -) :
- Rh- parent: Rh + or Rh- child
- Rh + parent (++): Rh + child
- Rh + parent (+ -): Rh + or Rh- child
Rh factor inheritance probabilities
As we can see, there are nine possibilities of genetic inheritance of Rh factor that give rise to different probabilities, as the case may be:
Now, about Rh incompatibility or Rh sensitization, it can only occur when the mother is Rh factor negative and the father is Rh positive (cases 4 and 7). If the baby inherits the Rh positive factor from the father, hemolytic disease of the newborn occurs. The mother’s immune system can “attack” the Rh factor positive red blood cells of the fetus causing anemia, jaundice and even fetal death. We have already detailed all this in detail when we explained what Rh incompatibility is.
In Babies and more | What Rh factor will the baby inherit? What blood group will my child have?
