Final answer:
The TCR beta chain possesses a D segment in its variable regions, while the TCR alpha chain does not.
Step-by-step explanation:
The T cell receptor (TCR) genes consist of variable (V), diversity (D), and joining (J) segments. The variable regions of the TCR alpha (α) chain possess multiple Vα and Jα segments, while the TCR beta (β) chain encompasses Vβ, Dβ, and Jβ segments. The D segment is present in the TCR beta chain only. These gene segments undergo genetic rearrangement during T cell development in the thymus to provide the necessary genetic diversity for the production of TCRs with unique antigen-binding regions.