Question:medium
The immunoglobulin antigenic determinant that changes in the variable region is the?
The immunoglobulin antigenic determinant that changes in the variable region is the?
Show Hint
Variable region equals the antigen-binding site, whose unique marker is the idiotype.
Updated On: Jun 24, 2026
- Idiotype
- Isotype
- Allotype
- Epitope
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Map each option to its location on the immunoglobulin to find the one tied to the variable region.
Step 2: The variable region holds the antigen-binding pocket, and the unique determinants there are called idiotypic determinants or idiotypes; they vary clone by clone because each clone binds a different antigen.
Step 3: By contrast, isotype and allotype both reside in the constant region, isotype marking the antibody class and allotype marking inherited allelic differences. Epitope describes a site on the antigen, so it does not fit the question at all.
Step 4: The variable-region determinant is therefore the idiotype.
\[\boxed{\text{Idiotype}}\]
Step 2: The variable region holds the antigen-binding pocket, and the unique determinants there are called idiotypic determinants or idiotypes; they vary clone by clone because each clone binds a different antigen.
Step 3: By contrast, isotype and allotype both reside in the constant region, isotype marking the antibody class and allotype marking inherited allelic differences. Epitope describes a site on the antigen, so it does not fit the question at all.
Step 4: The variable-region determinant is therefore the idiotype.
\[\boxed{\text{Idiotype}}\]
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