After working in the clinic window of the laboratory for so many years, I often encounter such a conversation: after several tubes of blood are pumped out, suddenly a person says, "Doctor, is it a blood test type?" After living so big, I still don't know my blood type! ".Once I was sent to a free clinic. I didn't think the blood type test program would be popular, because after all, you have to take blood from your fingertips and suffer from skin and flesh. I didn't expect a long queue before the blood test, which shows that everyone cares about their blood type. At present, with the popularity of social software such as WeChat, small games about psychological tests such as blood type, personality and IQ are also popular in the circle of friends. Today, we will talk about blood type and uncover the mystery of blood type inheritance.
What is blood type?
Blood type usually refers to the specific antigen type on the erythrocyte membrane. Narrow blood type refers to the difference of red blood cell antigen between individuals; Blood type in a broad sense refers to the antigen type on the surface of blood components (including red blood cells, white blood cells and platelets). At present, there are more than 30 blood types in human beings, and each blood type system is determined by genetic factors and has immunological characteristics. Everyone is most familiar with ABO blood group system and Rh blood group system, among which ABO blood group system is the most common, which is divided into four types: A, B, AB and O; Followed by Rh blood group system, divided into Rh positive and Rh negative; In addition, there are extremely rare blood group systems such as MNS and P. In clinical blood transfusion, ABO and Rh blood group systems must be compatible before blood transfusion. Blood of different blood types will produce serious hemolytic reaction, which is life-threatening. A special case is that AB type can accept blood transfusion of any blood type, which is called "universal recipient"; Type O can be transfused to people of any blood type, which is called "universal blood transfusion" and "abnormal blood transfusion". In fact, blood transfusion should be based on the principle of homologous blood transfusion. Allotypic blood transfusion will only be used in small quantities when absolutely necessary. Blood type is not only limited to ABO blood type and blood transfusion, but also has extensive practical value in anthropology, genetics, forensic medicine, transplant immunity, disease resistance (or susceptibility) and other disciplines, and research topics such as blood type and personality, blood type and IQ, blood type and life span are paid more attention to.
What is ABO blood type?
ABO blood group divides blood into four blood groups according to whether there are A and B antigens on red blood cells. Human serum of different blood types contains different antibodies, but does not contain antibodies against autologous red blood cell antigens. For example, people with type A blood have antigen A on their red blood cells, and their serum only contains anti-B antibodies. Among all ethnic groups in China, type A, type B and type O blood each account for about 30%, while type AB only accounts for about 10%.
ABO blood group antigen antibody
Rh blood group, the second largest blood group system
Rh blood group system is the second largest blood group system after ABO system, which means blood group system of rhesus monkey. Rh is the first two letters of mbth, a macaque. 1940, scientists such as Randsteiner found that rhesus monkeys and human red blood cells have the same Rh blood group antigen, so they were named. Rh blood group is the most complex blood group in human red blood cells. At present, more than 40 kinds of Rh antigens have been found, among which D antigen is the strongest. Those with D antigen on red blood cells are called Rh positive, and those without D antigen are called Rh negative. Rh-positive blood group accounts for about 99% of Han nationality and most ethnic minorities in China, and Rh-negative blood group only accounts for about 1%. However, among other ethnic minorities, there are many Rh-negative people, such as Miao and Tatar. The legendary "panda blood" refers to RH negative blood, which is called "panda blood" because it is very rare and extremely rare. In the Japanese TV series Blood Suspicion, which was popular in China in 1980s, Xing Zi Oshima, the heroine starring Yamaguchi Momoe, had extremely rare blood type, which led to many mysteries about her life experience.
Will parents with type A blood give birth to children with type O blood?
Knowing the genetic law of blood type will solve this problem. Under normal circumstances, blood type is lifelong, and the inheritance of blood type depends on chromosomes in cells. There are 23 pairs of chromosomes in human cells, and each pair of chromosomes consists of two single chromosomes, one from the father and the other from the mother. The main component of chromosome is deoxyribonucleic acid (DNA), which determines the genetic traits and functions. Each piece of DNA has unique genetic characteristics and functions, and these pieces are called genes. A small piece of DNA in the same position on two single chromosomes in a pair of chromosomes is called allele. The gene locus of ABO blood group system is located on chromosome 9. ABO blood group is controlled by three genes: A, B and O, and one * * can be combined into six pairs of alleles: AA, AO, BB, BO, AB and OO. If the alleles from both parents are the same, the chromosomes on somatic cells are homozygous (for example,1:the alleles on type A chromosome are A and A); If the contents of the contained genes are different, they are called heterozygotes (Example 2: Alleles on type A chromosome are A and O). Whether homozygote or heterozygote, the sum of genes on a pair of chromosomes is called inheritance. ABO blood group has six pairs of alleles, so there are six genetic models. For example, the genetic patterns of the above two cases are AA and AO respectively.
Since there are six gene types, why do we usually only know four ABO blood types?
This is because blood type actually refers to its expression. Not all inherited genes can be expressed, and the traits that can be expressed are called expression. The difference between the expression of blood type and heredity is that there are dominant genes and recessive genes. Some genes, whether homozygous or heterozygous, can show the traits they control. This gene is called a dominant gene. However, some traits controlled by genes can only be expressed when they are homozygous, but not when they are heterozygous. This gene is called recessive gene. In ABO blood group system, A and B genes are dominant genes, and O genes are recessive genes. For example, in a pair of chromosomes, one chromosome carries the A gene and the other chromosome carries the O gene. The allele combination is AO, the genetic formula is AO, and the expression is A (because A is the dominant gene and O is the recessive gene). This person's blood type is A, not O.
Both parents are type A, so it can be inferred that both father and mother have the possibility of inheritance of AA and AO blood types. If a child is born with both parents' chromosomes carrying O gene, then the allele combination of the child's chromosome is homozygous OO, which has the inheritance of OO and the expression of O, that is, the child's blood type is O type.
How to judge a child's blood type according to his parents' blood type
Say so much cold knowledge, isn't it a bit foggy? Then the dry goods come ~ ~ ~ If you know the blood type of your parents, you can simply sit in the right position according to a picture and judge the blood type that your child may or may not appear.
Genetic law of blood group
Knowing the truth of the genetic law of blood type, I believe that everyone will never ask the question "How can type A father and type B mother give birth to type O son?" Of course, it is unscientific to judge whether there is kinship by the way of "identification of blood relatives". However, with the rapid development of modern medical technology, paternity testing with red blood cell blood type can only be denied, but it is not certain (for example, if the child is type A and both parents are type O, then it can be inferred that the child is not born to the parents; However, both parents are O-type, and the children are O-type. It is not possible to judge that the children are the biological parents because of the consistency of O-type blood. The most reliable "consanguinity" is DNA parentage.
About the author: Shi Jiahua, Associate Research Fellow of Shanghai Huangpu District Health Examination Station.