This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'A 40 year old female patient complains of excessive bleeding. Patient gives a history of road traffic accident 5 hours ago and had a lacerated wound on lower back region. Blood grouping test reveals presence of antigen A and antigen B. This system for blood grouping consists of 3 major allelic genes which are located on- \nSelect and explain. \nA. Chromosome 8, B. Chromosome 9, C. Chromosome 10, D. Chromosome 7', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ABO system:\n\nThis system consist of 3 major allelic genes; those are A, B and O.\nThey are located on long arm of chromosome 9.\nThese genes control the synthesis of blood group antigens A and B.\nBased on presence\xa0or absence of antigen A and Antigen B, blood\xa0is divided into 4 groups i.e. A, B, AB and O.', 'role': 'assistant'}]