The process is somewhat more complex, since 10 to 20 short DNA segments, known as D, or diversity, segments are located between the H and J segments. The rearranged genes are then transcribed. A second transcription follows, whereby introns re removed and mRNA is formed and translated into specific Ig H chains. These gene segments obviously contribute significantly to the generation of hypervariablility in the V regions. When three segments of DNA randomly join to encode the entire H chain V region, they enhance the recombination possibilities.
H chains have five chains as previously described.
Each isotype and homology region is encoded by genes separated by intervening sequence or introns. Ifs us the same set of V region genes. Thus if the class or subclass is change, only the C region is switched.