Bombay phenotype

Bombay phenotype

[bombā′]

Etymology: Bombay, India, where first reported

a rare genetic trait involving the phenotypic expression of the ABO blood groups. The gene for the H antigen, which in the usual dominant form of HH or Hh is responsible for the precursor necessary for the production of the A and B antigens, is homozygous recessive in individuals with this trait so that the expression of the A, B, and H antigens is suppressed. Cells of such individuals are phenotypically of blood type O, and the serum contains anti-A, anti-B, and anti-H antigens. In such cases the offspring from two phenotypic O blood type parents may be blood type AB. The phenomenon is an example of the intricate interaction of linked genes in which one gene on a chromosome controls the expression or suppression of another gene that is not its allele. See also ABO blood group.