The determination of the human blood type is of high
importance when it comes to blood transfusion in case of an accident or
illness. Knowing the blood type of a person ensures that only donor blood is
used for transfusion which will not clump with the patient’s blood.
There are different characteristics which determine the
blood group. Best known is the AB0 system, which will be further investigated
in the following experiment.
The blood type is determined by a gene which occurs in three
alleles: A, B or 0. As humans are diploid, each person carries two of those
alleles. The combination results in the phenotypical blood type, where blood
type A can be coded by a genotype AA or A0, the phenotype B by BB or B0, having
the blood type AB is based on a genotype AB and 0 results from two alleles of
0, thus 00.
The blood type is characterized by two proteins. First, the
antigens present on the surface of red blood cells. They can be of type A
(blood group A) or B (blood group B), both can be present (blood group AB), or
none (blood group 0). Second, antibodies present in the blood serum. They are
opposed to the antigens on the blood cells, meaning that a person of blood type
A has got antibodies of type Anti-B. In the same way are Anti-A antibodies
present in the serum of a person with blood type B. As blood type AB has both
antigens present on the surface of the red blood cells, no antibodies are
present in the blood, whereas both kinds of antibody are present in blood of type
The binding of the antibodies in the serum to the antigens
on the red blood cells is called agglutination. As one antibody can bind two
antigens, many cells can clump together, which will eventually be lethal.
Nevertheless, the principle of agglutination is used in this
experiment. Depending on whether or not a blood sample clumps after addition of
known antibodies can reveal the blood type of unknown blood samples.
The hypothesis is thus that agglutination of a blood sample
with Anti-A represents a blood type A, agglutination with Anti-B represents a
blood type B, agglutination with both antibodies represents a blood type AB and
no agglutination with both antibodies represents a blood type 0.