Bombay Blood Group:
• Another gene , H is inherited independently of ABO. The H substance produced by H gene is precussor for A & B antigen.
• Therefore this gene is necessary for the synthesis of A & B antigen, & is present in 99.9% of population.
• The H gene may have silent allele h. In homozygous hh individual , even ABO genes are present , the precurssor for the synthesis of these antigens is not produced in absence of H gene.
• This rare blood group is called Bombay group (Oh) as it was discovered in this city.
• This blood phenotype was first discovered in Bombay, now known as Mumbai, in India, by Dr. Y. M. Bhende in 1952.
• The Bombay group is only a phenotypic expression because these individuals do possess ABO genes..
• If offsprings of bombay individual (hh) recieve an H gene from other parent they will exhibit normal AB antigens.
• Because A & B antigens are absent in bombay group individuals , they are typed as group O person with anti A & anti B sera.
Only anti -H can detect the bombay blood group. While other groups will give a positive reaction with anti H-serum, the bombay blood group will give a negative reactions.
• Se gene: is an another independent gene involved in ABO expression. Individulas possessing Se gene have respective A, B & H antigens ( according to their genotype.) in their secretion & body fuids such as saliva, tears, milk & urine..
• This person are called secretors & form about 80% of population. The non- secretor status is due to the presence of slient allele se (genotype sese) on both chromosomes.
• The Se locus encodes a specific fucosyltransferase that is expressed in the epithelia of secretory tissues, such as salivary glands, the gastrointestinal tract, and the respiratory tract. The enzyme it encodes catalyzes the production of H antigen in bodily secretions.
• "Secretors" have at least one copy of the Se gene that encodes a functional enzyme—their genotype is Se/Se or Se/se. They
secrete H antigen which, depending on their ABO genotype, is then processed into A and/or B antigens.
• Non-secretors are homozygous for null alleles at this locus (se/se). They are unable to produce a soluble form of H antigen and hence do not produce A and B antigens.
Biochemistry of H, A, & B antigen.
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