**Core Concept**
The question is testing the understanding of the structural differences between Apo B48 and Apo B100, which are the primary apolipoproteins of chylomicrons and VLDL, respectively. Apo B48 and Apo B100 are synthesized from a single gene, but they differ in their amino acid sequence and function.

**Why the Correct Answer is Right**
Apo B48 and Apo B100 are synthesized from a single gene through alternative RNA splicing, resulting in different mRNA transcripts. The difference in the primary structure of these two apolipoproteins is due to the presence of a unique amino acid sequence in Apo B48, which is not present in Apo B100. This unique sequence is a result of the alternative splicing of the Apo B gene, leading to the inclusion or exclusion of specific exons.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the difference in Apo B48 and Apo B100 is not due to the presence of different genes or gene mutations.
**Option B:** This option is incorrect because the size of the apolipoprotein is not the primary reason for the difference between Apo B48 and Apo B100.
**Option C:** This option is incorrect because the difference between Apo B48 and Apo B100 is not due to the presence of different receptors or binding sites.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that Apo B48 and Apo B100 have different functions in lipid metabolism, with Apo B48 primarily involved in the digestion and absorption of dietary lipids, and Apo B100 playing a crucial role in the regulation of cholesterol levels in the bloodstream.

**Correct Answer: C. Post-transcriptional modification through alternative RNA splicing.