Final answer:
The heavy chain of the B-cell receptor is indeed expected to undergo rearrangement before the light chain (Answer: a. True), which is necessary for producing the diversity of antibodies required for an effective immune response.
Step-by-step explanation:
The heavy chain of the B-cell receptor (BCR) undergoes rearrangement before the light chain. This process is essential for the B-cell development and its ability to produce a diverse array of antibodies.
In the development of B cells, the genomic rearrangement occurs as a multistep process that begins with the heavy chain (V, D, and J segments). An enzyme known as DNA recombinase is responsible for this rearrangement, ensuring that each B cell has a unique variable region capable of binding to a different antigen. Upon successful rearrangement of the heavy chain, the gene segments for the light chain (V and J segments) are then rearranged to complete the variable region of the BCR.
This process provides the means for generating millions of unique antigen-binding sites, which are crucial for the adaptability of the immune system to recognize and neutralize a vast array of pathogens. The subsequent splicing at the mRNA level further diversifies the possible combinations, contributing to the creation of over 106 potential antigen-binding sites and thus the ability for each B cell to express a distinct BCR and, upon activation, secrete unique antibodies.