Select the correct statement about adaptive immune recognition and gene generation mechanisms:

Introduction / Context:
Adaptive immunity relies on vast receptor diversity generated somatically. T-cell receptors (and B-cell receptors/antibodies) arise through V(D)J recombination, junctional diversity, and, for B cells, somatic hypermutation after activation. By contrast, MHC molecules are encoded by polymorphic germline genes without somatic rearrangement.

Given Data / Assumptions:

• TCR and BCR diversity mechanisms are compared to MHC genetics.
• Basic definitions of antigen, epitope, and lineage markers are assumed.

Concept / Approach:
TCR α/β chains are formed by recombining variable (V), diversity (D, beta chain only), and joining (J) segments with random N/P nucleotide additions. This produces a unique receptor per T cell. MHC genes are inherited and highly polymorphic but do not undergo somatic rearrangement. Not all T cells are CD4+; many are CD8+.

Step-by-Step Solution:

Verification / Alternative check:
Immunology texts detail RAG1/2-mediated recombination for TCR/BCR; MHC genes are non-rearranging, though polymorphic at the population level.

Why Other Options Are Wrong:

• CD4+ only: CD8+ cytotoxic T cells exist.
• Epitope vs antigen: An antigen contains many epitopes; not vice versa.
• MHC II rearrangement: Does not occur somatically.
• BCR fixed: BCRs undergo V(D)J recombination and, after activation, somatic hypermutation.

Common Pitfalls:

• Confusing population polymorphism (MHC) with somatic recombination (TCR/BCR).

Final Answer:
T-cell receptors (TCRs) are generated by random assortment and recombination of gene segments (V(D)J recombination)