Final answer:
The C regions of T-cell receptor β-chain loci differ from those of immunoglobulin heavy-chain loci in that TCRs typically have a single C region, whereas immunoglobulins have multiple isotypes corresponding to different antibody classes. Genetic rearrangement provides the diversity for both BCRs and TCRs, with the former having distinct constant regions for each antibody class.
Step-by-step explanation:
Unlike the C regions of immunoglobulin heavy-chain loci, the C regions of the T-cell receptor β-chain loci do not have multiple isotypes; TCRs typically have a single C region for each type of chain (alpha and beta). Both B cell receptors (BCRs) and T cell receptors (TCRs) undergo genetic rearrangement to achieve diversity in their antigen recognition domains. This rearrangement involves the combination of V (variable), D (diversity, which is only present in heavy chains and TCR β-chains), and J (joining) gene segments to generate unique antigen-binding sites. However, the immunoglobulin heavy-chain loci feature multiple C (constant) region isotypes, corresponding to different antibody classes (IgM, IgG, IgA, IgD, IgE), each with distinct roles and mechanisms of action within the immune response.
The generation of antibody diversity is critical for the immune system's ability to recognize a vast array of antigens. B cells achieve this through recombination of gene segments, while antigen-binding specificity is determined by the variable domains formed by the V, D, and J segments in heavy chains and V, and J segments in light chains. The T-cell receptor, while similar to antibodies in its structure, is less complex, and its diversity also arises through genomic rearrangement of V, D, and J gene segments.