This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Distinct amino acid sequence at the antigen combining site is called: 
Select and explain. 
A. Idiotype, B. Allotype, C. Epitope, D. Paratope
A: Idiotype
Answer: A: Idiotype 
Explanation: Ans. (a)Idiotype is based on antigenic difference in the hypervariable region.Allotype is based on alleleic difference in immunoglobulins e.g., Gm type.Isotype is antigenic differences in constant regions of heavy chain decide isotypes.