Question 5:
How much percentage of the human genome is represented by the exome?
The human exome represents about 1-2% of the total human genome, making option (C) 1 the most precise answer among the choices.
Correct Answer
(C) 1
The exome consists of all protein-coding exons across ~20,000-25,000 genes, totaling roughly 30-35 million base pairs out of the human genome’s ~3.2 billion base pairs. This equates to approximately 1% (or up to 2% including nearby untranslated regions), confirmed by sources like Wikipedia and NCBI. Despite its tiny size, exome mutations account for ~85% of disease-causing variants, prioritizing it in sequencing.
Option Explanations
| Option | Percentage | Explanation |
|---|---|---|
| (A) 4 | Too high | Exceeds the exome’s ~1-2% share; confuses with repetitive DNA (~45%) or gene-related regions broadly (~25%). |
| (B) 10 | Too high | Overestimates; total coding sequence is <2%, not 10%. |
| (C) 1 | Correct | Matches consensus: ~1% or 30 Mb of genome. |
| (D) 20 | Too high | Approximates protein-coding gene areas including introns (~20-25%), but exome excludes introns. |
Why It Matters
For exams like NEET or bioinformatics, knowing the exome’s 1% fraction highlights its efficiency in genetic research—sequencing it covers most Mendelian disease causes without full-genome cost. Recent projects like UK Biobank reinforce this ~1-2% benchmark.
