ABO system
Individuals may have blood from group A, B, AB or O, depending on the presence of certain antigens on red blood cells. Individuals with type A blood have agglutinogen A; B, agglutinogen B; AB, the two antigens mentioned, and O, none.
Blood plasma, in turn, can harbor two other proteins called anti-A agglutinins and anti-B agglutinins and they are responsible for the problems resulting from blood transfusions that do not observe compatibility blood. Individuals A have anti-B agglutinins; individuals B, anti-A; Type O blood individuals have both agglutinins and ABs none.
Got confused? Look at the chart:
*IA and IB are codominant and, thus, the dominance relationship between these three alleles is: IA = IB > i.
Looking at the scheme, it is understandable why blood A individuals receive blood from a type B (or vice versa) can have serious complications and why type AB individuals are considered recipients universals. Likewise, type O individuals are considered universal donors (with some caveats) due to the absence of agglutinogen.
MN System
In 1927, Landsteiner and Levine discovered two agglutinogens in human red blood cells, which they named M and N. They found that some people had one of these antigens, while others had both together. Thus, they considered three phenotypes: group M, group N and group MN, determined by a pair of alleles, with no dominance relationship:
LM (or M) gene - conditions the production of the M antigen;
LN (or N) gene - conditions the production of the N antigen.
Anti-M and anti-N antibodies are produced only when an individual in one group receives blood from an individual in the other group and, therefore, problems arising from the incompatibility of the groups only occur when such procedure is performed. times.
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Rh factor
The Rh system is controlled by genes independent of the ABO system genes. In this, a pair of allele genes is considered: “R” and “r”, the first being dominant and with presence of antigen, and the second, recessive and without antigen. Individuals with antigen belong to the Rh+ group and non-carriers belong to the Rh- group.
In 1940, Landsteiner and Wiener discovered this system from the blood of the Rhesus monkey (Macaca mulatta). The blood of this animal, once injected into guinea pigs or rabbits, caused the synthesis of antibodies (anti-Rh agglutinins) in them, which could promote the agglutination of the donated blood.
Rh factor discoverers extracted serums containing anti-Rh agglutinins from guinea pigs and rabbits. Then they mixed the serum with blood from different people and found that, in some cases, the red blood cells agglutinated, indicating the presence of the Rh factor in human blood: people Rh+. In other cases, the red blood cells did not agglutinate, indicating the absence of the Rh factor in the blood: Rh- people.
Rh- individuals will only present antibodies if they receive Rh+ red cells. When transfusing blood from an Rh+ donor to an Rh- recipient, agglutination of the donated red cells may not occur. However, in a second blood transfusion of this type, it may cause agglutination of the donated red cells due to the accumulation of agglutinins, which can promote the agglutination of the donor's red blood cells and cause obstruction of blood capillaries and even death.
By Mariana Araguaia
Graduated in Biology
Would you like to reference this text in a school or academic work? Look:
ARAGUAIA, Mariana. "Inheritance of blood groups"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/heranca-grupos-sanguineos.htm. Accessed on June 28, 2021.
