This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Genetics, Subject name: Biochemistry
ApoB 48 & ApoB 100 is synthesized from them RNA; the difference between them is due to: 
Select and explain. 
A. RNA splicing, B. Allelic exclusion, C. Deamination of cytidine to uridine, D. Upstream repression
C: Deamination of cytidine to uridine
Answer: C: Deamination of cytidine to uridine 
Explanation: Ans. C. Deamination of cytidine to uridine(Ref: Harper 31/e page 390)An example is the apolipoprotein B (apoB) gene and mRNA.In the liver, the single apo B gene is transcribed into an mRNA that directs the synthesis of apo B100.In the intestine, the same gene directs the synthesis of the primary transcriptA cytidine deaminase converts a CAA codon in them RNA to UAA at a single specific siteRather than encoding glutamine, this codon becomes a termination signal apo B48 is the result.