<prompt> Effector binding region of the antibody isConstant region of heavy chainVariable region of heavy chainConstant region of heavy and light chainVariable region of heavy and light chain  <response>: Within the variable regions of both the Light and Heavy chains are subregions consisting of extremely variable amino acid sequences, called hypervariable, that cooperate in space to form the antigen-binding siteReference: Jawetz, Melnick, Adelbergs Medical Microbiology; 27th edition; Chapter 8; Immunology 