Practice question

ABO antigens represent terminal glycosylation differences on H precursor anchored glycolipid or glycoprotein paragloboside type two chain precursor. H synthesis requires FUT1 alpha one two fucosyltransferase attaching fucose galactose beta1-4 GlcNAc forming Fuc alpha1-2 Gal structure. Functional A allele encodes alpha one three N acetylgalactosaminyltransferase GTA adding GalNAc galactose H forming A trisaccharide GalNAc alpha1-3(Fuc alpha1-2)Gal antigen A. B allele encodes alpha one three galactosyltransferase GTB adding galactose forming B trisaccharide Gal alpha1-3(Fuc alpha1-2)Gal antigen B. O allele harbors two six one delG frameshift producing truncated soluble inactive enzyme lacking catalytic domain so H remains unconverted due absent transferase activity producing O phenotype H antigen only. O individuals therefore lack A B glycosyltransferases but retain FUT1 FUT2 fucosyltransferases required Bombay phenotype hh. Misstatements Type A adding galactose or Type B lacking modification incorrect. Genetics explains transfusion reactions anti A anti B IgM natural antibodies isoagglutinins and Bombay phenotype hh lacking fucosyltransferase producing no H substrate requiring Bombay blood donations extremely rare compatible blood type cases.