Flexi Says: The antigen receptors produced by lymphocytes are complex proteins. Each type of antigen receptor is made of several polypeptide chains. Each polypeptide chain is encoded by one gene. The human genome contains genes for hundreds of polypeptide chains that can be included in antigen proteins. Various combinations of these polypeptides can produce an enormous variety of specific antigen receptors. Additionally, more variety is introduced by a process called junctional diversification that occurs when stem cells produce new lymphocytes. In this process, the ends of the gene segments can be shortened or lengthened. These "on the fly" changes in the genetic code create a larger variety of polypeptides.
