To know the blood group our baby will have It is not as simple as knowing parent groups. Usually a blood test should be performed to determine what blood group we have, however you cannot know with a simple analysis the complete genotype of the sample owner, that is, we do not know what genes we have exactly and there are three types or variants of the gene that determines the blood group.
For that reason, although we can get an idea of Blood type that our baby will have, we cannot know simply by knowing the group that the parents have. We must go deeper or make an approach to the possibilities.
Mendel's laws
Blood groups are determined by inheritance, following Mendelian laws. It is the genes that encode them and in the case of the blood group, it will be determined by the alleles (variants of the same coding gene) that both parents possess and their combination in the gametes that give rise to the new being.
I know it can be complicated at the beginning, especially if we have forgotten the rudiments of genetics that we study at school. Genes and chromosomes are in pairs.
The gene that determines the blood group has three variants and their combinations in the couple will give rise to different blood groups. When they combine two identical genes, the group is pure. But when the combination is of two different alleles or variants of the gene, we find a hybrid.
Dominant and recessive alleles
The gene that determines the Blood type It has three variants or alleles: A, B and O. Each person has two alleles, from their father and 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.
The hybrids will be from the blood group of the most dominant allele, in this case A or B, but they can have an O allele that does not manifest but that can be transmitted to the offspring when passing to one of the gametes, which are haploid (i.e. they only have one set of genes, not the double set that the rest of the cells have).
When conceived the baby will receive the alleles that carry the gametes, that is, the ovule and sperm. You will receive one from your father and one from your mother, but it does not necessarily have to be the one that dominated your parent.
Each parent will transfer their child one of their two alleles, which are called IA, IB and ii (corresponding to group O). The possible combinations between the four inheritable alleles give us 16 possibilities, which will determine the inherited group
What blood type will my son have?
People who have an AB must necessarily have in their two alleles one corresponding to A (called IA) and one from B (IB). It will not transmit inheritance from group O. A person with type O has neither the A allele nor the B allele. It has two alleles ii (those corresponding to group O).
But it's not that simple, well the alleles are dominant (A and B) or recessive (O) , so that a group A or B can be presented in a person carrying the allele O in combination of A and B.
There are actually, therefore, genotypes corresponding to AO (IAi) and BO (IBi), which are manifested in the blood group of the dominant allele (A or B), but which can pass the recessive allele to the child. When cell division occurs, it may happen that one type O is inherited and, in combination with another hybrid, there is a possibility that the child is O despite the fact that the group of parents is A and B.
What could not happen is that an individual AB has a child with group O, since he does not possess the recessive allele corresponding to the group O to transmit and the allele i is recessive in combination with AI or IB.
Conclusion
The inheritance of the blood group It is determined by a gene that has three manifestations or alleles. The different possible combinations between them will determine, at random, the transmitted allele and the final combination, which will be the one that place the baby's blood group. Since not all of us have very fresh mathematical combinations or Mendel's laws, we will see more concrete examples of possible combinations and inheritance.
