A blood group is a characteristic of a person's blood composition, or rather, the content of certain antigens in plasma and erythrocytes. There are four blood groups, they are passed from parents to children according to certain rules. Knowing the blood types of the parents, it can be assumed which group the child will get, and vice versa.
Characteristics of blood groups
Until the beginning of the 20th century, blood transfusion was a risky business: in half of the cases it gave excellent results and cured the sick, and in half the condition of the people worsened to death. In 1900, Karl Landsteiner conducted experiments by mixing the blood of different people. He noticed that in some cases the red blood cells seem to "stick together" with each other, resulting in clots, in other cases this did not happen. The scientist studied the structure of red cells and found that different people have a different composition of blood - it may contain substances called A and B, or it may not. Depending on the composition, he identified four blood groups.
The first group does not contain any antigen - neither A nor B. The second includes only substance A, the third - B. In the fourth, both antigens are present. This fact makes it possible to understand the mechanisms of inheritance of blood groups and quickly determine what composition of erythrocytes can be in a child born to parents with a certain blood composition.
Blood type inheritance
When considering the inheritance of blood composition, it is important to understand that if the parents do not have a specific substance in the blood, then the child will not inherit it either. In addition, when inheriting different antigens, different results can be obtained, since the genes responsible for substances A and B are equally dominant, and the absence of antigens is a recessive allele. In total, there are 36 variants of inheritance of blood groups.
If you find it difficult to understand genetic laws, on the Internet or textbooks on biology and genetics, you can find tables with a complete description of the inheritance of blood groups.
If both parents have the first blood group, then the child will have nowhere to get either antigen A or antigen B - he will also be born with the same group. When combining the first, which does not possess these substances, and the second, with antigen A, two results can be obtained: either the antigen is inherited, forming the second group, or it is not transmitted to the child, and his blood will be of the first group. There are no other options - the child cannot inherit substance B.
The same applies to the third group - in this case, there is nowhere to get antigen B.
The most unpredictable result is obtained when the second and third groups are mixed: they have both antigens, so a child can be born with any group - the substances may not be inherited, only one antigen or both will be transmitted. If the wife has the first group, and the husband has the fourth (or vice versa), then in half of the cases a child is born with the second group (antigen A is inherited), and in half - with the third (antigen B is transmitted). The first type of blood is impossible in this case, since the allele responsible for the absence of substances in erythrocytes is recessive.
