Title: Organization and expression of immunoglobulin genes
Content:  Heavy chain contains similar gene segments such as VH, JH and CH, but also has another gene segment called D (diversity). Unlike the light chain multigene family, VDJ gene segments code for the variable region of the heavy chain. The rearrangement and reorganization of gene segments in this multigene family is more complex. The rearranging and joining of segments produced different end products because these are carried out by different RNA processes. The same reason is why the IgM and IgG are generates at the time.
Title: Organization and expression of immunoglobulin genes
Content:  The light chain gene has three gene segments. These include: the light chain variable region (V), joining region (J), and constant region (C) gene segments. The variable region of light is therefore encoded by the rearrangement of VJ segments. The light chain can be either kappa,κ or lambda,λ. This process takes place at the level of mRNAs processing. Random rearrangements and recombinations of the gene segments at DNA level to form one kappa or lambda light chain occurs in an orderly fashion. As a result, "a functional variable region gene of a light chain contains two coding segments that are separated by a non-coding DNA sequence in unrearranged germ-line DNA" (Barbara et al., 2007).
Title: Somatic genome processing
Content:  Local rearrangements affect specific loci only. Such rearrangements, for instance, help create genes that produce a great variation of immunoglobulins in vertebrates. During life, organisms have contact with a large number of antigens. Which means that the immune system needs to synthesize a wide range of antibodies. Each immunoglobulin is a tetramer consisting of four polypeptides connected by disulfide bridges. They form two long heavy chains and two short light chains. But vertebrate genome does not code entire genes of heavy and light immunoglobulins, only gene segments. Segments of heavy chain are located on chromosome 14, they include 11 constant gene segments (CH), that are preceded by 123-129 variable segments (VH), 27 diversity gene segments 
Title: Antibody
Content:  The chromosomal region that encodes an antibody is large and contains several distinct gene loci for each domain of the antibody—the chromosome region containing heavy chain genes (IGH@) is found on chromosome 14, and the loci containing lambda and kappa light chain genes (IGL@ and IGK@) are found on chromosomes 22 and 2 in humans. One of these domains is called the variable domain, which is present in each heavy and light chain of every antibody, but can differ in different antibodies generated from distinct B cells. Differences, between the variable domains, are located on three loops known as hypervariable regions (HV-1, HV-2 and HV-3) or complementarity-determining regions (CDR1, CDR2 and CDR3). CDRs are supported within the variable domains by conserved framework regions. The heavy chain locus contains about 65 different variable domain genes that all differ in their CDRs. Combining these genes with an array of genes for other domains of the antibody generates a large cavalry of antibodies with a high degree of variability. This combination is called V(D)J recombination discussed below.
Title: V(D)J recombination
Content: The immunoglobulin heavy locus (IGH@) on chromosome 14, containing the gene segments for the immunoglobulin heavy chain. ; The immunoglobulin kappa (κ) locus (IGK@) on chromosome 2, containing the gene segments for part of the immunoglobulin light chain. ; The immunoglobulin lambda (λ) locus (IGL@) on chromosome 22, containing the gene segments for the remainder of the immunoglobulin light chain. Human antibody molecules (including B cell receptors) are composed of heavy and light chains, each of which contains both constant (C) and variable (V) regions, genetically encoded on three loci: Each heavy chain or 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 
Title: Hypervariable region
Content:  In antibodies, hypervariable regions form the antigen-binding site and are found on both light and heavy chains. They also contribute to the specificity of each antibody. In a variable domain, the 3 HV segments of each heavy or light chain fold together at the N-terminus to form an antigen binding pocket.
Title: IGH@
Content: IGHV1-2, IGHV1-3, …, IGHV1-69-2, IGHV2-5, …, IGHV7-4-1 IGHD1-1, IGHD1-7, …, IGHD7-27 IGHJ1, IGHJ2, IGHJ3, IGHJ4, IGHJ5, IGHJ6 Heavy chain alpha (IgA): IGHA1, IGHA2 Heavy chain gamma (IgG): IGHG1, IGHG2, IGHG3, IGHG4 Heavy chain delta (IgD): IGHD Heavy chain epsilon (IgE): IGHE Heavy chain mu (IgM): IGHM Symbols for variable (V) immunoglobulin gene segments start with IGHV and include two or three numbers separated by dashes. Examples:  Symbols for diversity (D) immunoglobulin gene segments start with IGHD and include two numbers separated by dashes. Examples:  Symbols for joining (J) immunoglobulin gene segments:  Symbols for constant region (C) immunoglobulin genes:     
Title: DNA repair protein XRCC4
Content:  light chain and contains approximately 300 gene segments for the variable region, V, four J segments than encode a short protein region, and one constant, C, segment. To produce a light chain with one unique type of VL, when B cells are differentiating, DNA is rearranged to incorporate a unique combination of the V and J segments. RNA splicing joins the recombined region with the C segment. The heavy chain gene also contain numerous diversity segments, D, and multiple constant segments, Cμ, Cδ, Cγ, Cε, Cα. Recombination occurs in a specific region of the gene that is located between two conserved sequence motifs called recombination signal sequences. Each motif is flanked by a 7 bp 
Title: Antibody
Content:  Somatic recombination of immunoglobulins, also known as V(D)J recombination, involves the generation of a unique immunoglobulin variable region. The variable region of each immunoglobulin heavy or light chain is encoded in several pieces—known as gene segments (subgenes). These segments are called variable (V), diversity (D) and joining (J) segments. V, D and J segments are found in Ig heavy chains, but only V and J segments are found in Ig light chains. Multiple copies of the V, D and J gene segments exist, and are tandemly arranged in the genomes of mammals. In the bone marrow, each developing B cell will assemble an immunoglobulin variable region by randomly selecting and combining one V, one D and one J gene segment (or one V and one J segment in the light chain). As there 
Title: Immunoglobulin heavy chain
Content:  The immunoglobulin heavy chain (IgH) is the large polypeptide subunit of an antibody (immunoglobulin). In human genome, the IgH gene loci are on chromosome 14. A typical antibody is composed of two immunoglobulin (Ig) heavy chains and two Ig light chains. Several different types of heavy chain exist that define the class or isotype of an antibody. These heavy chain types vary between different animals. All heavy chains contain a series of immunoglobulin domains, usually with one variable domain (VH) that is important for binding antigen and several constant domains (CH1, CH2, etc.). Production of a viable heavy chain is a key step in B cell maturation. If the heavy chain is able to bind to a surrogate light chain and move to the plasma membrane, then the developing B cell can begin producing its light chain. The heavy chain doesn't always have to bind to a light chain. Pre-B lymphocytes can synthesize heavy chain in the absence of light chain, which then can allow the heavy chain to bind to a heavy-chain binding protein.

Question: which gene segments code for the variable region of the heavy chain?
Answer: V.