Final answer:
The V regions in immunoglobulin heavy-chain genes consist of gene segments V, D, and J that undergo gene rearrangement to form a transcribable exon, enabling the immune system to create diverse antibodies.
Step-by-step explanation:
The V regions in immunoglobulin heavy-chain genes are composed of V (variable), D (diversity), and J (joining) gene segments. These segments undergo gene rearrangement to generate a transcribable exon. This process is a crucial part of the immune system's ability to create a diverse array of antibodies, which are necessary for recognizing and binding to a wide range of antigens.
The V region variability is provided by the hypervariable regions, also known as complementarity-determining regions (CDRs), which form the antigen-binding surface. The creation of diverse antibodies is further enhanced by somatic hypermutation, although the process itself was not the correct choice in the multiple-choice question presented. Additionally, the variable regions are subject to allelic exclusion, ensuring that each B cell expresses a single antibody specificity.