The somatic mutations in a V region gene are confined to the one linked to the C region gene. Why is it logical that IgM not possess these mutations and that only the classes that are generated after...

The somatic mutations in a V region gene are confined to the one linked to the C region gene. Why is it logical that IgM not possess these mutations and that only the classes that are generated after IgM possess them? Hypothesize a mechanism for splicing the V, J, D, and C regions together based on the sequences and spacings between the flanking conserved nucleotides of these regions.