Figure 2. Schematics of heavy and light chain allele configurations during primary and editing rearrangements.

a. Heavy chain rearrangement in mouse and man. At the pro-B cell stage, B cells undergo D to J rearrangement on both alleles (DJ/DJ). This is followed by V to DJ rearrangement on one or both alleles. The allele genotypes are: DJ, DJ_s (secondary DJ_H rearranged allele; also included here but not shown are alleles that have undergone D-D fusion), H+ (productive VDJ rearrangement), H− (non-productive VDJ rearrangement), V_HR (V_H replacement). Black arrows indicate primary rearrangement attempts. Green arrows indicate secondary rearrangements in B cells with one or more prior non-productive rearrangements and red arrows indicate editing rearrangements in B cells with one or more prior productive rearrangements. b. Light chain rearrangements in mouse. B cells initially have both κ and λ loci in the germline configuration (κ⁰/κ⁰, λ⁰/λ⁰). Most B cells rearrange κ first (VκJκ) then undergo RS rearrangement and, if needed, progress to λ rearrangement. Arrows indicate rearrangement attempts using the same color scheme as in panel a. Shown is only one of many possible orderings of L chain rearrangement. To save space, only the loci that are undergoing rearrangement are shown. κ+ (productive κ light chain gene rearrangement), κ− (non-productive κ rearrangement), RS (RS deletion or inversion by either V-RS or iRS rearrangement), λ+ (productive lambda light chain rearrangement), λ−(non-productive lambda rearrangement).