The doctor has been a doctor for a long time, always encounter all kinds of interesting things and interesting questions. This time, there is another father with a heavy face and anxiety asking for help: “Dr. Zhang, the child’s mother is type A, I am type B, how come the child is type O? Is this child my biological child or not? Is it the wrong baby? Should I go for personal identification?” Today we will talk about the little secret of blood type. How is blood typed? Usually, the blood type we refer to is the type of specific antigen (a protein) on the red blood cell membrane, and humans have several blood group systems, but the most closely related to clinical practice and well known is the ABO blood group system. The ABO blood group is based on the presence of antigen A or antigen B on the red blood cell membrane and divides the blood into four blood types: A, B, O and AB. If there is only antigen A on the red blood cell is type A blood, only antigen B is type B blood, if there is both A antigen and B antigen principle is AB blood, these two antigens are not for O blood. Our people of all ethnic groups, A, B and O blood types accounted for about 30%, AB type accounted for about 10%. What is the possible blood type of a child born to parents with different blood types? Blood type is inherited with the help of chromosomes in cells. Each pair of chromosomes in human cells is composed of two single chromosomes, one from the father and the other from the mother. Therefore, the blood type system is inherited from the mother and father, but it is not simply the same as the father or mother’s blood type, and may even be different from both of them. If a parent has an O and a B type, the child’s blood type may be O or B. If a parent has an O and an AB type, the child’s blood type may be different from the parent’s, and each of them may be 50% A or B type. To sum up, the law of inheritance of blood type is shown in the following chart: So the father in front and other dads who have this doubt, you can rest assured! Doctors have to help solve family conflicts! However, there are always exceptions to the rule of inheritance, and the above-mentioned rule of inheritance only refers to the vast majority of cases. Occasionally, we may encounter individuals who do not conform to this rule of inheritance, and may encounter the phenomenon of “cis-AB” inheritance, but the probability of this special case is very, very small, and lower than the lottery hit rate.