there are two types of polypeptide chains responsible for the biological and immunological properties of the different immunoglobulins, the heavy chain and the light chain; they are linked by covalent and non-covalent forces to give a four-chain Y-shaped structure based on pairs of identical heavy and light chains; each chain consists of a variable region and a constant region which are coded for by different genes; some immunoglobulin classes occur as polymers of this basic monomer.