Dictionary of Human Evolution and Biology

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O Null Allele

Lack of antigenic specificity that characterizes the O in the ABO blood group. It consists of four precursor sugars attached to glycoproteins of the cell membrane, aka H substance; it is missing a fifth terminal sugar that would he attached by an enzyme, but the enzyme is nonfunctional. This null product differs from its homologues that attaches the A- and B-specific sugar by a critical frame shift substitution that makes it a null product.

See A anti-gen and B antigen.

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