<P> Each heavy chain and light chain gene contains multiple copies of three different types of gene segments for the variable regions of the antibody proteins . For example , the human immunoglobulin heavy chain region contains 2 Constant ( Cμ and Cδ ) gene segments and 44 Variable ( V ) gene segments , plus 27 Diversity ( D ) gene segments and 6 Joining ( J ) gene segments . The light chains also possess 2 Constant ( Cμ and Cδ ) gene segments and numerous V and J gene segments , but do not have D gene segments . DNA rearrangement causes one copy of each type of gene segment to go in any given lymphocyte , generating an enormous antibody repertoire ; roughly 3 × 10 combinations are possible , although some are removed due to self reactivity . </P>
which gene segments code for the variable region of the heavy chain
V