W.B.C.S. Main 2018 Question Answer – Zoology – Bombay Phenotype.

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1)What is BOMBAY PHENOTYPE?

Bombay Phenotype

It is important to be cautious in predicting the ABO blood type of children based on the phenotypes of their parents. This is due to the fact that a third antigen (H) on the surface of red cells can prevent the expected ABO blood type from occurring.Continue Reading W.B.C.S. Main 2018 Question Answer – Zoology – Bombay Phenotype.

Normally, if an A blood type mother has an O type child, the father is expected to be type O or at least to carry the O allele (OO, AO, or BO genotype).

schematic drawings of phenotypes and genotypes of an expected ABO inheritance pattern

The child has inherited an O allele from both parents. However, an O blood type child can also be born to parents who do not have the O allele if a recessive form of the allele for the H antigen also is inherited from both parents.

schematic drawings of phenotypes and genotypes of an ABO Bombay inheritance pattern

The H antigen is a precursor to the A and B antigens. For instance, the B allele must be present to produce the B enzyme that modifies the H antigen to become the B antigen. It is the same for the A allele. However, if only recessive alleles for the H antigen are inherited (hh), as in the case above, the H antigen will not be produced. Subsequently, the A and B antigens also will not be produced. The result is an O phenotype by default since a lack of A and B antigens is the O type. This seemingly impossible phenotype result has been referred to as a Bombay phenotype pronounce word because it was first described in that Indian city.

The ABO blood system is further complicated by the fact that there are two subtypes of type A and two of AB. These are referred to as A1, A2, A1B, and A2B.

There is an antigen named as H Antigen or H substance present in all RBCs of ABO blood groups. This antigen is the precursor substance on which A-B-O genes operate to produce A and B antigens. All of these antigens are glycoproteins chemically. H antigen is L- Fucose structurally. A antigen is formed by the addition of N -acetylgalactosamine while B is formed by the addition of Galactose to H antigen. In people with O blood group this antigen simply remains unmodified. In addition to RBCs these antigens are also present in almost all tissues of the body. So in terms of H antigen a person has H/H or H/h blood group.

Now this H antigen is almost ubiquitously present and is not ordinarily important in blood grouping or blood transfusion.

But Bhende et al from Bombay reported a rare case where these A,B and H antigens were absent from red cells. This H antigen deficiency was named after Bombay (the place where it was first reported) as Bombay Phenotype. It is also referred to as OH/hh blood group.

It has a prevalence of 1 in 10,000 individuals in India and 1 in a million people in Europe. Serum of these individuals contain anti-A, anti-B and anti-H antibodies. So they can accept blood only from their own blood group, otherwise a severe reaction will be triggered.

This blood group also poses problem during confirming paternity with blood group matching. A person with Bombay Phenotype will give an impression as having O blood group but his blood will show transfusion reaction when mixed with blood having O group.

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