<P> In 1987, Susumu Tonegawa was awarded the Nobel Prize in Physiology or Medicine "for his discovery of the genetic principle for generation of antibody diversity". </P> <P> Human antibody molecules (and B cell receptors) are composed of heavy and light chains (each of which contains both constant (C) and variable (V) regions), which are encoded by genes on three loci: </P> <Ul> <Li> The immunoglobulin heavy locus (IGH @) on chromosome 14, containing the gene segments for the immunoglobulin heavy chain . </Li> <Li> The immunoglobulin kappa (κ) locus (IGK @) on chromosome 2, containing the gene segments for part of the immunoglobulin light chain . </Li> <Li> The immunoglobulin lambda (λ) locus (IGL @) on chromosome 22, containing the gene segments for the remainder of the immunoglobulin light chain . </Li> </Ul> <Li> The immunoglobulin heavy locus (IGH @) on chromosome 14, containing the gene segments for the immunoglobulin heavy chain . </Li>

Recombination centres and the orchestration of v(d)j recombination