V - C Regions Through DNA Splicing -
As indicated above, the second phase of DNA rearrangement involves association of a V segment with a C segment. It has been shown that the same V segment can attach with different C regions, thus providing for H-chain class switching.

This is achieved by successive deletions of DNA, leading to the production of IgM in primary response and IgG and IgA as a secondary immune response.

IgM has all heavy chains, while in IgG3, segment C is missing and in IgG1, C μ and C4γ3 arc missing Further deletions may occur.