We talked yesterday about the way in which the blood group is inherited from the parents. The existence of the four blood groups is due to the existence of three alleles or varieties of a gene that determines the formation of certain antigens in the blood cells. Let's see some concrete examples of how this inheritance occurs.
Let us take this issue as a clarification for those who have doubts about inheritance according to Mendel's laws, which will determine the possible combinations of alleles and their dominance.
Let's see concrete examples. To understand them it is necessary to review the previous article, which explains the way in which the three variants of the gene that determines the blood group can appear in humans.
Examples of inheritance of blood groups
A pure AA person (IAIA) who has children with another AA can only have children with group A and IAIA alleles. There is no possible new combination, since whatever the allele the gamete carries will always be an AI.
But if it is an AO (IAi), it has Blood type A but an O allele that can be transmitted in gametes, who has children with another AO (IAi), their children can be AA, AO and even OO, which means that they have a 25% chance that their descendants have the group O blood and a 75% chance of having a group A, in some cases pure (25%) and in others mixed (50%). The same would happen with two people with mixed alleles and blood of group B.
The children of a cigar A with a cigar B will always be AB, but if one of them is a hybrid, the possible combinations of the alleles are greater. There will never be an O group among their children since, although it inherits the i (O) allele of one of the parents, it will always be recessive in combination with A or B.
In the case of two hybrids, one with group A and one with group B, we find a quarter of possibilities for each blood type: A, B, AB and O. The allelic series that determines blood groups is determined by three genes : A, B and O. The genes A and B are codominant and the O is recessive (A = B> O).
If one of the parents is from a pure group A or B and has children with an OO, these will always be AO, with a blood group A. However, if one of the parents is AB and the other OO, the chances will be 50% of children with group A and 50% of group B, in both cases mixed AO and BO. What cannot be is a child with group O, since the allele he inherits is always recessive in combination with A and B.
A mixed AO that has children with an AB, will have a 50% chance of having children with blood group A, of which 25% is pure and the other mixed AO. Another 25% chance is that an AB is born and the remaining 25% would be from a group B, if the B allele is combined with the O. The same percentages will be presented in the case of a BO with an AB, but counting that gene B will be the most present in the possible combinations.
Blood Group Inheritance Calculator
The most complex cases are those that include mixed alleles in parents, and require mathematical calculations to determine, but also, we can use an online calculator that offers the possibility of calculating the possibilities in each couple.
Conclusion
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 transmit randomly, one of the two alleles that they have in their genetic endowment, which will be represented in the gamete, ovule and sperm. For that reason children of the same couple may have different blood groups, depending on the allele transmitted by each parent.
I hope with these examples of blood group inheritance Let's better understand how this system works. The topic is fascinating and we will continue talking about it, on the next occasion about the origin of the blood groups, its extension in the human groups, to better understand how they influence our lives.
In Babies and more | What blood group will my child have ?, Blood groups, genetics: genes and chromosomes
