A rare human variant of the ABO blood group system (first discovered in Bombay, India) that does not have A, B, or O antigens. Individuals homozygous for an autosomal recessive allele (h/h) cannot make the precursor H substance (q.v.) from which the A and B antigens are formed. This is a classical case of recessive epistasis in human genetics, because without the product of allele H, the products of the ABO locus cannot be formed. Bombay bloods appear to be group O when routinely tested by antibodies against the A or B antigens, but an individual with the Bombay phenotype may be carrying unexpressed genes for the A and/or B antigens. However, they make anti-H that is not found in individuals of groups A, B, or O. Therefore it is possible for a child of group A or B to be produced from parents that appear to be group O, if one of them is a Bombay phenotype and carries the genes for antigens A or B or both. See A, B antigens.
Subjects: Genetics and Genomics.