Are you sure that you have O? Or it may be Bombay O…

Amanda, science 1 Comment

Have you ever known that there are 2 universal donors of blood? Yes there are. The famous O- and now the Bombay Blood type which was first discovered in Bombay (now Mumbai) India in 1952 by Dr. Bhende and his colleagues.

This blood type differs from the other blood types in the absence of certain antigens (Proteins) in our blood. This represents the 3 different types of blood in human population. The type of the antigen is decided by a certain gene.

One of the genes that codes for the proteins determining blood type is called the ABO gene. IA, IB and i are 3 different alleles of this gene. Though there are 3, your blood type antigen is decided by only 2 alleles which inherit one from your mother and the other from your father.

To have an O type child, both parents should pass on the i allele. If both parents don’t possess at least one i allele, then it is impossible to have an O type child.

But what if they give birth toan O type child? If such a situation occurs, the child possibly carries Bombay blood type.

This occurs due to H antigen which is located on the surface of red blood cells and is the precursor of A and B antigens. Both IA and IB allele are needed to produce a transferase enzyme to modify the H antigen into A and B antigens.

For type O individuals, the H antigen cannot be transformed further because no functional transferase enzyme is produced to modify the antigen which is why type O individuals become universal donors. All the blood types have this H antigen except in Bombay blood type. Therefore even if the parents don’t possess any i allele if they pass on the homozygous recessive H allele (hh) to the child then the child possesses the Bombay blood type.

Courtesy - http://readgenetics.blogspot.com/2013/05/hh-antigen-system-bombay-blood.html
Courtesy – http://readgenetics.blogspot.com/2013/05/hh-antigen-system-bombay-blood.html

In a blood type test the Bombay blood type is classified as O type; as there are no antigens in O type so do the Bombay blood type. In a blood transfusion it is very important to classify the correct blood group specially the O type and Bombay O type. O type can produces antibodies against A and B antigens but Bombay O type can produce antibodies against both A and B as well as the H antigen.

Blood Type Antigens Present Antibodies in Serum
A A,H B
B B,H A
AB A,B,H None
O H A,B
Bombay None A,B,H

If a Bombay O type person is classified as O type in a blood transfusion; giving O type blood causes to produce antibodies in recipient’s blood against the H antigen, in donor’s blood. The antibodies of the Bombay blood react with the red blood cells of the donor and causes cell death. Since they have antibodies against H, A, and B antigens, they can only receive blood from Bombay blood type people.

The probability of finding a person with Bombay blood type is 0.0004% of world human population. India has the highest number of people with the Bombay blood group where there is 0.01316% of Indians. If you have O type blood group even if it is positive or negative there is a probability of 0.0004% you to have the Bombay blood type.

Free advice: If you checked your blood type long before, it’s better to confirm if it is definitely O.

References – http://genetics.thetech.org/ask/ask413

http://www.brighthub.com/science/genetics/articles/34637.aspx

Image source – http://fc08.deviantart.net/fs50/i/2009/310/3/e/Bloodcells_by_Krodil.jpg