<prompt> Which of the following is true about isotypic variation?Subtle amino acid changes due to allelic differenceChanges in a heavy and light chain in variable regionChanges in heavy and light chain in constant region responsible for class and subtypeThese are areas in antigen that bind specifically to antibody  <response>: Ans c Changes in heavy and light chain in constant region responsible for class and subtype Ref. Ananthanarayan 8e, p 01; DR Arora 3e p 119 Isotopic specificities The antigenic specificities which distinguish between the different classes and subclasses of immunoglobulin present in all individual of a species,. e.g. Antigen specificity of IgA and IgG. They are located on Constant domains of Ig chains in all individual. Other immunoglobulin Specificity Idiotypic specificity - Specificity of greatest biological impoance is idiotypic specificity, peaining to the nature of antigen binding site. These are located on V region. Allotypic-specificity - Antigenic specificity which distinguishes immunoglobulins of the same class, between different groups of individual in the same species. 