Karl Landsteiner discovered the ABO blood group system in 1900. He found that mixing blood samples together could cause agglutination, or clumping. Based on this, he identified the main blood groups: A, B, AB, and O. The presence of antigens A or B on red blood cells determines blood group. Rh factor is another important blood group - a person can be either RhD positive or negative. Blood typing involves testing blood against different antibodies to identify a person's blood group. Matching donor and recipient blood by ABO and RhD type is crucial for safe blood transfusions.

1. Blood Groups
1. ABO BLOOD GROUPING SYSTEM
2. RH FACTOR

2. How blood group is determined !
 As per Mendel, every character is controlled by one pair of alleles. There are only two
optional forms, one of which is Dominant and the other one is Recessive. Cases are
observed where there are more than two optional forms of a gene for one character.
Thus when three or more alleles are responsible for a single characteristic, they are
known as multiple alleles. All these alleles occupy the same specific locus on the
chromosomes. In a diploid cell, only two alleles can be present at a time on the
homologous chromosomes. A well known example is the ABO blood type in humans.
 There are 4 main blood groups (types of blood) :–
 A, B, AB and O. Your blood group is determined by the genes you inherit from your
parents.
 Each group can be either RhD positive or RhD negative, which means in total there are 8
blood groups.
 Rh was First discovered in Rhesus Monkey , That’s why called Rhesus Factor

3. Blood genotypes
Here the inheritance is based on three
alleles i.e. IA , IB , i . IA and IB are
dominant and i is recessive. The gene
for producing antigen I and it’s allele for
non producing antigen is i . IA is
responsible for producing Antigen-A.
Gene 1B is responsible for producing
Antigen-B.
These two alleles are co-dominant
which means that both can express
themselves in presence of each other.
Thus three alternatives are possible.
Various persons in different blood
groups can have following probable
genotype.

4. To work out your blood group, your red cells are
mixed with different antibody solutions. If, for
example, the solution contains anti-B antibodies and
you have B antigens on your cells (you're blood
group B), it will clump together.
If the blood does not react to any of the anti-A or
anti-B antibodies, it's blood group O. A series of
tests with different types of antibody can be used to
identify your blood group.
If you have a blood transfusion – where blood is
taken from one person and given to another – your
blood will be tested against a sample of donor cells
that contain ABO and RhD antigens. If there's no
reaction, donor blood with the same ABO and RhD
type can be used.
Blood group Serum test

5. In practice of blood transfusion. Karl Landsteiner discovered the ABO blood group in 1900 when he separated
cellular and liquid components from both his and his colleagues’ blood mixed in combination. As indicated by the
negative symbol (-) in the table , no agglutination of red blood cells was observed when both components from the
same individuals were mixed. However, RBC agglutination was observed in some combinations, as indicated with
the positive symbol (+). From the results gleaned from his studies, Landsteiner realized that people could be
grouped depending on the agglutination pattern of their RBCs. For example, Dr. St. and Mr. Land. belong to one
group. Similarly, Dr. Plee. and Mr. Zar. belong to a disparate second group, and Dr. Sturl. and Dr. Erdh belong to a
third group. In the next year, a fourth group was discovered by Sturle and von Decastello, Landsteiner's colleagues,
and these four groups became what is now known as the ABO group system (A, B, AB, and O groups). However, the
most important finding obtained from these experiments is that only ABO-matched blood that does not cause RBC
agglutination should be used for transfusion.
Experiment

6. In order to explain the RBC agglutination phenomenon, Landsteiner postulated that 2 different
antigens (A and B) are found on the surface of RBCs, and the "naturally occurring" antibodies
against these antigens are found in the plasma of individuals who do not express them (The
Landsteiner’s Law). For example, blood group A individuals express the A antigen on their RBCs
and possess anti-B antibodies in their plasma. Similarly, blood group B individuals express the B
antigen on their RBCs and possess anti-A antibodies in their plasma. Blood group AB individuals
express both A and B antigens on their RBCs and possess neither anti-A nor anti-B antibodies,
whereas blood group O individuals express neither A nor B antigens on their RBCs but possess
both anti-A and anti-B antibodies.
ABO blood groups are hereditary, and their mode of inheritance was explained by Bernstein’s one
gene-three allelic model. In this model, Bernstein postulated that there are three alleles, A, B, and
O, at a single ABO genetic locus, and that A and B alleles are co-dominant against the recessive O
allele. This produces 6 genotypes (AA, AO, BB, BO, AB, and OO) resulting in 4 phenotypes.
Landsteiner’s discovery

7.  Pregnant women are always given a blood group test. This is because if the
mother is RhD negative but the child has inherited RhD-positive blood from
the father, it could cause complications if left untreated.
RhD-negative women of child-bearing age should always only receive RhD-
negative blood.
Rhesus disease is uncommon these days because it can usually be prevented
using injections of a medication called anti-D immunoglobulin.
Pregnancy

8. Giving blood
 Most people are able to give blood, but only 1 in 25 people actually do. You can donate
blood if you:
 are fit and healthy
 weigh at least 50kg (7st 12lb)
 are 17-66 years old (or 70 if you've given blood before)
 are over 70 and have given blood in the last 2 years