Question

In ABO system a person has
A. 3 alleles
B. 2alleles
C. Multiple alleles
D. No alleles

Answer 1

Karl Landsteiner reports for the first time the ABO blood group in humans. Blood types A, B and O were discovered by Landsteiner while blood group AB was discovered by de Castello and Steini . Alleles are an alternative form of a gene. There are two types of alleles, dominant and recessive or wild and mutant types. Mendel found only two forms of the gene for the seven characters he examined in peas.

Complete answer:
Human blood can be divided into several blood group systems, i.e. ABO blood type, MN blood group and Rh blood group.
ABO system of blood grouping
Blood type control genes contain information about the specific properties of sugar molecules present on the surface of erythrocytes along with glycoproteins. The sugar molecule determines the specificity of the antigen.

There are three types of alleles, IA, IB and IO. for this gene. The proteins produced by the IA and IB alleles are called A antigens and B antigens.
-People with blood group A have the A antigen on the surface of their erythrocytes and antibodies to the B antigen in their plasma.
-People with blood group B have B antigens on red blood cells and antibodies to A antigen in their plasma.
-People with AB blood have both the A and B antigens on their red blood cells, and no antibodies to any of these antigens in their plasma.
-Type O individuals are free of the A and B antigens in their erythrocytes, but have antibodies to both antigens in their plasma .

Hence, the correct answer is option (A).

Note: People with blood type AB can receive blood from group A, B , AB and O blood groups that's why they are known as universal recipients.
People with blood type O can donate blood to anyone that's why they are known as universal donors.
When a blood transfusion is carried out between an incompatible donor and recipient, the reaction of antigens to cells and antibodies in the plasma results in the formation of clots that block capillaries.
A protein called the rhesus antigen is found on the surface of red blood cells in many people. It was discovered by Landsteiner and Wiener in the blood of rhesus monkeys, hence the name. Depending on the breed.