Definition: a rare recessive trait at a locus that ordinarily manufactures H substance, the precursor from which the A and B phenotypes are elaborated; the mutant causes failure to produce H substance and no matter what the genotype at the ABO locus, the phenotype is O. The Bombay phenomenon is epistatic to the ABO locus.
[Bombay, India, where first reported]
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Examples: glitazone, GI cocktail, etc.