Recombination of heavy chain genes

The Heavy chains are synthesized in an analogous manner but are encoded through four gene segments that are, V, J, D and C in above figure. In humans, there are 51 V_H segments 27 D_H segments where D for diversity and H for heavy and six J_H segments.  Therefore, where the

Figure: The light chain variable region is encoded by two separate gene segments, V and J. The heavy chain variable region is encoded by three gene segments, V, D and J.

variable region of a light chain polypeptide  is encoded through V and J segments the variable region of a heavy chain is encoded via V, D and J segments. In humans connecting any of D, V, and J segments generates 51×27× 6 = 8262 probable heavy chain variable regions. In heavy chain gene system, there are also various   C segments, one for each class of heavy chain; Cµ, Cδ, the several Cγ    subclasses, Cε   and Cα  encoding  µ  ,α, ε, γ and δ heavy chain constant regions respectively. During lymphocyte maturation, two heavy chain gene rearrangements happen. First a chosen DH segment joins a JH segment (D_J joining) and then the recombined DHJH joins a chosen VH segment (VD_J joining).

Figure: Somatic recombination to create a human    light chain gene and expression of that gene to produce   light chain polypeptides.

For the assembly  of both light chain and heavy chain genes, the ends of the several DNA segments  to be joined can also undergo  modification  in during   the recombination  procedure  and this modifies  existing  codons  at these  junctions  or even  establish  new  codons,  therefore  increasing  antibody  diversity  since  further.  Additionally, antibody genes exhibit a higher than normal rate of mutation.