A common classification of blood groups is the AB0 system. Let's see how a child's blood group is inherited and what are the options if the parents have the same or different groups, as well as how the Rh factor is inherited.
Read about how to do an analysis to determine the blood group of a child in another article.
Mendel's law
Mendel studied the transfer of genes from parents to offspring, as a result of which he made conclusions about how certain traits are inherited. He formalized these conclusions in the form of laws.
He learned that a child receives one gene from each parent, so the child has one gene in a pair of genes for the mother and the other for the father. In this case, the inherited trait may appear (it is called dominant) or not (it is recessive).
With regard to blood groups, Mendel found out that genes A and B are dominant (they encode the presence of antigens on the surface of erythrocytes), and gene 0 is recessive. This means that when genes A and B are combined, both genes will encode the presence of agglutinogens, and the blood group will be the fourth. If genes A and 0 or B and 0 are transferred to the child, then the recessive gene will not appear, respectively, in the first case there will be only agglutinogens A (the child will have group 2), and in the second - agglutinogens B (the child will have the third group) ...
AB0 system
This system for the typology of blood groups began to be used since 1900, when the presence in the blood (on erythrocytes) of antigens, which were called agglutinogens, and antibodies to them, which began to be called agglutinins, were discovered. Agglutinogens are A and B, and agglutinins are designated as alpha and beta. Possible combinations of such proteins create 4 groups:
- 0 (first) - contains alpha agglutinin and beta agglutinin.
- A (second) - contains beta agglutinin and A agglutinogen.
- B (third) - contains alpha agglutinin and B agglutinogen.
- AB (fourth) - contains A agglutinogen and B agglutinogen.
Rh-factor system
In 1940, another protein was discovered on the surface of red blood cells, which was called the rhesus of the blood. It is determined in about 85% of people, marked as Rh +, and the blood of such people is called Rh-positive. In the remaining 15% of people, this antigen is not detected in the blood, their blood is Rh-negative and is designated as Rh-.
If mom and dad have the same blood types
Even if the blood group of the mother and father is the same, due to the possible carriage of the recessive gene 0, the baby may have several blood group variants.
If mom and dad have different blood types
With a different group, the parents will have even more gene transfer options.
Rh factor inheritance
This protein is inherited according to the dominant principle, that is, its presence is encoded by the dominant gene. For example, if this gene is designated with the letter D, then the genotype DD or Dd is possible in an Rh-positive person. With genotype dd, the blood will be Rh negative.
Possible options table
What is the probability of mutation?
A mutation, as a result of which a parent from the fourth group can have a child with the first group, occurs in 0.001% of cases. There is also the so-called Bombay phenomenon (its name is due to its frequent identification in Indians), according to which a child may have genes A or B, but they do not appear phenotypically. The frequency of this phenomenon is 0.0005%.
