This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'Which of the following statements is true about isotypic variation? \nSelect and explain. \nA. These result due to subtle amino acid changes resulting from allelic differences, B. These result due to changes in amino acid in heavy and light chain at variable region, C. Changes in heavy and light chain in constant region is responsible for class and subclass of immunoglobulins, D. These are areas in antigen that bind specifically to antibody', 'role': 'user'}, {'content': "Answer: C \nExplanation: Antibody genes also re-organize in a process called class switching that changes the one type of heavy chain Fc fragment to another, creating a different isotype of the antibody that retains the antigen specific variable region. This allows a single antibody to be used by different types of Fc receptors, expressed on different pas of the immune system. Ref: Ananthanarayan & Parker's textbook of microbiology 9th edition pg: 94", 'role': 'assistant'}]