In the entire genome, the exonic DNA constitutes
**Core Concept**
The question is testing the student's knowledge of the distribution of exonic and intronic DNA within the human genome. Exonic DNA refers to the coding regions of genes, while intronic DNA is non-coding and found within introns.
**Why the Correct Answer is Right**
Exonic DNA constitutes a small fraction of the total genome, approximately 1.2%. This is because most of the genome is composed of non-coding regions, including introns, regulatory elements, and repetitive sequences. The remaining 98.8% is composed of intronic DNA, which does not encode proteins but plays a crucial role in gene regulation and splicing. The ratio of exonic to intronic DNA varies across different species and is an important aspect of comparative genomics.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a percentage or a fraction, making it an ambiguous choice.
* **Option B:** This option is incorrect because it does not accurately reflect the proportion of exonic DNA in the human genome.
* **Option C:** This option is incorrect because it suggests that exonic DNA constitutes a larger fraction of the genome than it actually does.
**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the proportion of exonic to intronic DNA is: "1.2% coding, 98.8% non-coding". This highlights the importance of non-coding regions in the human genome and serves as a reminder of the vast difference in size between coding and non-coding DNA.
**Correct Answer:** C. 1.2%