Somatic hypermutation is the process by which the 40 V-genes, five J-genes, and 23 D-genes are combined and evolved to better bind specific targets. The mechanism targets residues unevenly, favoring hotspots (including CDRs), and also includes V(D)J recombination. Nowak et al. (1) calculate that human organism can produce distinct antibodies. This happens after class switching from IgM to IgG.
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1.
Nowak J, Baker T, Georges G, Kelm S, Klostermann S, Shi J, et al. Length-independent structural similarities enrich the antibody CDR canonical class model. mAbs. 2016;8(4):751–60. Available from: https://doi.org/10.1080/19420862.2016.1158370