Question

Which of the following is NOT a postulate of the clonal selection theory regarding the T- and B-cells _____

a. only the lymphocyte whose receptor bind strongly to their ligand get activated
b. individual lymphocyte bears only one type of receptor with a unique specificity
c. each lymphocyte bears a B-cell receptor (BCR) and a T-cell receptor (TCR)
d. lymphocytes binding to self molecules are eliminated early on in development
e. activated lymphocytes will expand and all the daughter cells will have the same specificity

Answer 1

Among the listed postulates of the clonal selection theory, the incorrect one is that each lymphocyte bears both a B-cell receptor and a T-cell receptor; actually, B-cells have only BCRs and T-cells have only TCRs.

Step-by-step explanation:

The clonal selection theory, as it pertains to T- and B-cells, includes several key postulates. First, only lymphocytes whose receptors bind strongly to their ligand (in this case, an antigen) become activated (a). Second, individual lymphocytes bear only one type of receptor with unique specificity to a particular antigen (b). Third, lymphocytes binding to self molecules are usually eliminated early in development, ensuring self-tolerance (d). Last, activated lymphocytes undergo clonal expansion, and all daughter cells retain the same antigen specificity as their parent cell (e). The incorrect postulate among the options provided is that each lymphocyte bears both a B-cell receptor (BCR) and a T-cell receptor (TCR) (c). In reality, a B-cell expresses BCRs and a T-cell expresses TCRs, but not both on the same cell.