Final answer:
Light chain rearrangements in pre-B cells are facilitated by DNA recombinase which splices various V and J segments to create over 106 unique VJ combinations, resulting in a unique variable chain for each differentiated B cell.
Step-by-step explanation:
Light Chain Rearrangements in Pre-B Cells
Light chain rearrangements in each of the 100 small pre-B cells occur through a process of gene segment excision and splicing performed by an enzyme called DNA recombinase. In the variable region of the germ-line B cell light chain gene, there are 40 variable (V) and five joining (J) segments. The DNA recombinase randomly excises and then splices one V segment to one J segment.
After RNA processing where additional splicing occurs, over 106 possible VJ combinations can arise, contributing to the diversity of the B-cell receptor (BCR) repertoire. Consequently, each differentiated B cell has a unique variable chain. The constant domain, which does not participate in antigen binding, remains the same for all antibodies.