<prompt> Immunoglobulin isotype class switching is determined by -Constant region of light chainConstant region of heavy chainVariable region of light chainVariable region of heavy chain  <response>: 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 Ref: Ananthanarayan Parkers textbook of microbiology 9th edition pg: 96 