Among the many techniques used in forensic science are those that involve the specific immunological recognition of a protein (the antigen). The protein molecule that recognizes an antigen is called an antibody.

An antigen-antibody reaction is exquisitely specific. This permits the unequivocal detection of a protein. As well, some antigen-based methods are highly sensitive, and so permit the quantification of very small amount of the protein antigen.

Antibodies are also referred to as immunoglobulins (Igs). Specific genes for antibodies direct the construction of antigen specific regions of the antibody molecule. Such antigen-specific regions are located at the ends of the arms of the Y-shaped immunglobulin molecule. The central core of the immunoglobulin is more constant in construction....