Final answer:
Productive light chain rearrangement in B cell development leads to the creation of a functional B cell receptor, which is crucial for clonal expansion and the immune response.
Step-by-step explanation:
If light chain rearrangement is productive, meaning it occurs without any errors and the resulting antibody can be expressed, it leads to the production of a functional B cell receptor. This is a key step in B cell development, as the functional B cell receptor is needed for the B cell to participate in the immune response. When B cells successfully produce a functional B cell receptor, it signifies that the B cell is mature and can recognize specific antigens, which is essential for its role in the adaptive immune system. Additionally, this step is crucial for clonal expansion, ensuring that B cells with functional receptors are ready to proliferate and mount an immune response when an antigen is encountered.