Existence four a blood type was proved by scientists at the beginning of the twentieth century. Researches showed that the blood type of the child will depend on a blood type of parents, that is it is inherited genetically.
What blood types exist
As a result of researches of the Austrian scientists of Karl Landshtayner and his pupils A. Shturli and A. Von Dekastello the system of classification of blood under the name "AB0" which is used still was created. According to this system there are four blood types:
I (0) - is characteristic absence in blood of special substances of it - antigens A and B; II (A) - are present at it antigens A;
III (AV) - is characterized by presence of antigens of type B; IV (AV) - in blood is antigens A and B.
This opening helped to exclude losses at blood transfusions as because of various characteristics blood of the donor could do harm to the patient's organism.
What blood type the child will have
In further researches by scientists it was proved that the child and other genetic signs will have identical principles of receiving a blood type. According to Mendel's laws formulated in the second half of the nineteenth century, parents with the first blood type make children without antigens A and B (that is, having the first blood type). The parents having the second blood type have children with the first or with the second blood type. At spouses with the third blood type children with the first or third blood type are born. At the parents having the first or second, or first and third blood types children from one of the specified groups are born. If one of spouses has the fourth group, the child cannot have the first blood type. If one of spouses has the first group, they cannot have a child with the fourth blood type. At spouses with the second and third group children with any blood type are born.
Principles of inheritance of a Rhesus factor of blood
Rhesus factor is called antigen (protein) which is on a surface of erythrocytes. It is present at blood approximately at 85% of people, that is they are a Rhesus factor - positive. In the absence of this antigen speak about a Rhesus factor - negative blood. These factors designate by the letters Rh: negative with the sign "minus", positive with the sign "plus".
If both parents have a negative Rhesus factor, at them the child only with Rhesus factor-negative blood can be born.
The positive Rhesus factor is prepotent sign, and negative - recessive. If both parents at a genotype have both signs, they will have a positive Rhesus factor. However in this case there is a probability (25%) that the child in this case will have a negative Rhesus factor. That is, if both parents or one of them have a positive Rhesus factor, they can have a child and about a Rhesus factor - positive, and with Rhesus factor-negative blood.