This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Blood group antigen NAG transferase present but galactosyltransferase is absent in \nSelect and explain. \nA. Group A, B. Group B, C. Group AB, D. Group Q', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A and B antigens are glycoproteins that differ in their terminal sugar.Under the influence of A or B genes, HAg is conveed into A or B antigen. Individuals with A gene express A transferase that catalyzes placement of a terminal N-acetylgalactosamine on H antigen to form A antigen.Those with B gene express B transferases that place a terminal galactose on the H antigen to form B antigen. Type AB individuals have both transferases.Ref: Textbook of medical physiology by N Geetha, 3rd edition, page no. 134', 'role': 'assistant'}]