Source:http://linkedlifedata.com/resource/umls/id/C0017351
NCI: This region represents the germline organization of the immunoglobulin heavy chain locus. The locus includes V (variable), J (joining), diversity (D), and C (constant) segments. During B cell development, a recombination event at the DNA level joins a D segment with a J segment; a V segment is then joined to the D-J gene. The C segment is later joined by splicing at the RNA level. Recombination of many different V segments with several D and J segments provides a wide range of antigen recognition. Additional diversity is attained by junctional diversity, resulting from the random additional of nucleotides by terminal deoxynucleotidyltransferase, and by somatic hypermutation, which occurs during B cell maturation in the spleen and lymph nodes. (from LocusLink),MSH: Genes and gene segments encoding the IMMUNOGLOBULIN HEAVY CHAINS. Gene segments of the heavy chain genes are symbolized V (variable), D (diversity), J (joining), and C (constant).