We have identified insertional mutants of mannosidase 1A and xylosyltransferase 1A in Chlamydomonas reinhardtii. To verify a knockout/knockdown of the enzymes in the insertional mutant strains, PRM measurements were performed. Mass spectrometric analyses of intact N-glycopeptides revealed that disruption of the genes altered the N-glycan composition of the alga (in single as well as double mutant).