Is it really accurate to drop blood to recognize relatives?

In China's ancient traditional drama, there is a play called Three Drops of Blood, which is about two families fighting for a child, and it is said that this child is the offspring of their own family. He went to the government because of the dispute. The presiding judge dripped the blood of the child together with the blood of each parent to see if it would converge, so as to correctly judge the biological parents of the child.

This play is about the blood type we mentioned above. The content described in classical drama is not consistent with the scientific content mastered by modern science.

Modern science has proved that according to the genetic theory of modern genetics, the identification of ABO blood type of offspring and the identification of parents with the same blood type can not determine who is the father of the child, but can deny whether a person is the father of the child. Here, we can understand this truth from the following table.

Parents' blood types, blood types that children may have, and blood types that children cannot have: A×AA, OB, ABA×BA, B, AB, OA×ABA, B, ABOA×OA, OB, ABB×BB, OA, ABB×ABA, B, ABAB× OA. If the child's blood type is type A, then his parents' blood types may be A×A, A×B, A×AB, A×O, B×AB, AB×AB, AB×O, with so many possibilities, it is difficult to absolutely tell what blood type his parents should be. Therefore, it is impossible to determine who the child is by blood type test.

On the contrary, if the child's blood type is B, then his parents will never have B or AB; Similarly, the child is type A and the parents will never be type A. In this case, it is possible to deny who is not the child's parents by blood type. This may be useful in some cases. For example, sometimes in the hospital, children are accidentally held by mistake, or the tag is hung wrong. Sometimes you can use this method to make a judgment and find your biological parents.

ABO blood group system is not only of great significance in blood transfusion, but also has the above applications in practical work. So, what is the significance of MN blood type in practical work? The blood type of MN system is far less important than that of ABO system in clinic. But it is of great significance in forensic medicine. The forensic doctor can judge who is the murderer according to the blood type of MN in the blood.