V-J rearrangements at Ig light chain (IgL) genes occur in resting small pre-B cells. In the absence of cell division, the probability of productive κ and λ rearrangements is proportional to the output of κ+ B and λ+ B cells in bone marrow. The kinetics and probability of productive κ or λ rearrangements was assessed in three groups of mice carrying two (wild-type), one or no intact Ig gene, and the following conclusion are drawn,κ and λ rearrangements occur independently at different kinetics, and rearrangements are initiated at a time when κ rearrangements are stopping. The probability of productive κ and λ rearrangements per chromosome is calculated to be −60 and −20% respectively. Thus, a κ gene can attempt rearrangements up to three times per chromosome during B cell development. These findings explain that the observed ratio of κ+ B/λ+ B cell production in wild-type mice is 95/
