Final answer:
The C regions of T-cell receptor β-chain loci are similar, unlike the varying C regions of immunoglobulin heavy-chain loci which correspond to different antibody classes with distinct functions.
Step-by-step explanation:
The constant (C) regions of the T-cell receptor (TCR) β-chain loci are similar, unlike the C regions of immunoglobulin heavy-chain loci. In the immunoglobulin molecules, each C region corresponds to a different antibody class, having a different number of constant domains, which determine the immunological mechanism of action of the corresponding antibody class. For instance, IgG molecules, which are a category of antibodies, consistently have three constant domains, while IgM and IgE have four. In contrast, the TCR has a more uniform structure with a constant C region across different TCRs.