tokens: Two human beta - 1 , 6 - N - acetylglucosaminyltransferases forming the core 2 O - glycan branch , C2GnT and the I antigen , IGnT , are homologous to each other in three regions of the catalytic domain ( A , B , C ) and their genes reside at the same locus , chromosome 9 , band q21 ( Bierhuizen , M . F . A . , Mattei , M . - G . and Fukuda , M . , Genes Dev . , 7 , 468 - 478 , 1993 ) .