Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes (red blood cells). For human blood transfusions, it is the most important of the 48 different blood type (or group) classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of June 2025. A mismatch in this serotype (or in variou Bl… Individuals with the rare Bombay phenotype (hh) produce antibodies against the A, B, and O groups and can only receive transfusions from other hh individuals. The table above summarizes the various blood groups that children may inherit from their parents. Genotypes are shown in the second column and in small print for the offspring: AO and AA both test as type A; BO and BB test as type B. The four possibilities represent the combinations obtained when one allele is taken… Historically, ABO blood tests were used in paternity testing, but in 1957 only 50% of American men falsely accused were able to use them as evidence against paternity. Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations, such as Bombay phenotype and cis AB. The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes (red blood cells). For human blood transfusions, it is the most important of the 48 different blood type (or group) classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of June 2025. A mismatch in this serotype (or in various others) can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant. Such mismatches are rare in modern [It] may be said that there exist at least two different types of agglutinins, one in A, another one in B, and both together in C. The red blood cells are inert to the agglutinins which are present in the same serum. Thus, he discovered two antigens (agglutinogens A and B) and two antibodies (agglutinins — anti-A and anti-B). His third group (C) indicated absence of both A and B antigens, but contains anti-A and anti-B. The following year, his students Adriano Sturli and Alfred von Decastello discovered the fourth type (but not naming it, and simply referred to it as "no particular type"). In 1910, Ludwik Hirszfeld and Emil Freiherr von Dungern introduced the term 0 (null) for the group Landsteiner designated as C, and AB for the type discovered by Sturli and von Decastello. They were also the first to explain the genetic inheritance of the blood groups. Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The I designation stands for isoagglutinogen, another term for antigen. The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34). The IA allele gives type A, IB gives type B, and i gives type O. As both IA and IB are dominant over i, only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B. IAIB people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous (IBi and IAi). The cis-AB phenotype has a single enzyme that creates both A and B antigens. The resulting red blood cells do not usually express A or B antigen at the same level that would be expected on common group A1 or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group. Individuals with the rare Bombay phenotype (hh) produce antibodies against the A, B, and O groups and can only receive transfusions from other hh individuals. The table above summarizes the various blood groups that children may inherit from their parents. Genotypes are shown in the second column and in small print for the offspring: AO and AA both test as type A; BO and BB test as type B. The four possibilities represent the combinations obtained when one allele is taken from each parent; each has a 25% chance, but some occur more than once. The text above them summarizes the outcomes. Historically, ABO blood tests were used in paternity testing, but in 1957 only 50% of American men falsely accused were able to use them as evidence against paternity. Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations, such as Bombay phenotype and cis AB. The same study also identified 18 rare alleles, which generally have a weaker glycosylation activity. People with weak alleles of A can sometimes express anti-A antibodies, though these are usually not clinically significant as they do not stably interact with the antigen at body temperature. Cis AB is another rare variant, in which A and B antigens are transmitted together from a single parent. ABO blood group incompatibilities between the mother and child do not usually cause hemolytic disease of the newborn (HDN) because antibodies to the ABO blood groups are usually of the IgM type, which do not cross the placenta. However, in an O-type mother, IgG ABO antibodies are produced and the baby can potentially develop ABO hemolytic disease of the newborn. ABO at BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH Encyclopædia Britannica, ABO blood group system National Blood Transfusion Service

The Rh blood group system is a human blood group system. It contains proteins on the surface of red blood cells. After the ABO blood group system, it The Rh blood group system is a human blood group system. It contains proteins on the surface of red blood cells. After the ABO blood group system, it is most likely to be involved in transfusion reactions. The Rh blood group system consists of over 50 defined blood group antigens, of which the five antigens D, C, c, E, and e are among the most prominent. There is no d antigen. Rh(D) status of an i The D antigen is inherited as one gene (RHD) (on the short arm of the first chromosome, p36.13–p34.3) with various alleles. Typically, Rhesus positive people have an intact RHD gene while negative people lack the gene (or have mutations in it). However, there are exceptions: for instance, Japanese and black Africans may have an intact gene that is not expressed or only at very low levels. The gene codes for the RhD protein on the red blood cell membrane. D− individuals who lack a functional RHD gene do not produce the D antigen and may be immunized by D+ blood. The D antigen is a dominant trait. If both of a child's parents are Rh negative, the child will definitely be Rh negative. Otherwise, the child may be Rh positive or Rh negative, depending on the parents' specific genotypes. The epitopes for the next 4 most common Rh antigens, C, c, E and e are expressed on the highly similar RhCE protein that is genetically encoded in the RHCE gene, also found on chromosome 1. It has been shown that the RHD gene arose by duplication of the RHCE gene during primate evolution. Mice have just one RH gene. The RHAG gene, which is responsible for encoding Rh-associated glycoprotein (RhAG), is found on chromosome 6a. The polypeptides produced from the RHD and RHCE genes form a complex on the red blood cell membrane with the Rh-associated glycoprotein. The Rh blood group system has two sets of nomenclature: one developed by Ronald Fisher and R. R. Race, the other by Wiener. The two systems reflect different theories of inheritance. The Fisher–Race system uses the CDE nomenclature. This system is based on the theory that a separate gene controls the product of each corresponding antigen (e.g., a "D gene" produces D antigen, and so on). However, the d gene was hypothetical, not actual. The Wiener system uses the Rh–Hr nomenclature. This system is based on the theory that there is one gene at a single locus on each of the two copies of chromosome 1, each contributing to production of multiple antigens. In this theory, a gene R1 is supposed to give rise to the "blood factors" Rh0, rh′, and rh″ (corresponding to modern nomenclature of the D, C, and E antigens) and the gene r to produce hr′ and hr″ (corresponding to modern nomenclature of the c and e antigens). Notations of the two theories are used interchangeably in blood banking (e.g., Rho(D) meaning RhD positive). Some consider that Wiener's notation is more complex and cumbersome for routine use. DNA testing has shown that both are partially correct: There are in fact two linked genes, the RHD gene which produces a single immune specificity (anti-D) and the RHCE gene with multiple specificities (anti-C, anti-c, anti-E, anti-e). Thus, Wiener's postulate that a gene could have multiple specificities (something many did not give credence to originally) has been proved to be correct. On the other hand, Wiener's theory that there is only one gene has proved to be incorrect, as has the Fisher–Race theory that there are three genes, rather than the two. The CDE notation used in the Fisher–Race nomenclature is sometimes rearranged to DCE to more accurately represent the co-location of the C and E encoding on the RhCE gene, and to make interpretation easier. The hemolytic condition occurs when there is an incompatibility between the blood types of the mother and fetus. There is also potential incompatibility if the mother is Rh negative, and the father is positive. When the mother conceives for the first time, with a positive child, she will become extremely sensitive. When any incompatibility is detected when she conceives the second time in less than two years then, the mother often receives an injection at 28 weeks' gestation and at birth to avoid the development of antibodies towards the fetus. If not given, then the baby will be dead and must be aborted. These terms do not indicate which specific antigen-antibody incompatibility is implicated. The disorder in the fetus due to Rh D incompatibility is known as erythroblastosis fetalis. The D antigen is inherited as one gene (RHD) (on the short arm of the first chromosome, p36.13–p34.3) with various alleles. Typically, Rhesus positive people have an intact RHD gene while negative people lack the gene (or have mutations in it). However, there are exceptions: for instance, Japanese and black Africans may have an intact gene that is not expressed or only at very low levels. The gene codes for the RhD protein on the red blood cell membrane. D− individuals who lack a functional RHD gene do not produce the D antigen and may be immunized by D+ blood. The D antigen is a dominant trait. If both of a child's parents are Rh negative, the child will definitely be Rh negative. Otherwise, the child may be Rh positive or Rh negative, depending on the parents' specific genotypes. The epitopes for the next 4 most common Rh antigens, C, c, E and e are expressed on the highly similar RhCE protein that is genetically encoded in the RHCE gene, also found on chromosome 1. It has been shown that the RHD gene arose by duplication of the RHCE gene during primate evolution. Mice have just one RH gene. The RHAG gene, which is responsible for encoding Rh-associated glycoprotein (RhAG), is found on chromosome 6a. The polypeptides produced from the RHD and RHCE genes form a complex on the red blood cell membrane with the Rh-associated glycoprotein.