Whole-Exome vs Whole-Genome Sequencing: What Each Covers

What Exome Sequencing Reads

Whole-exome sequencing uses capture probes to enrich the protein-coding exons before sequencing. Because it targets a small fraction of the genome, it can achieve deep coverage of coding regions at moderate cost.

It reliably detects coding point mutations and small insertions and deletions, and gives a genome-wide view of the coding mutation load, but its capture is uneven and it covers non-coding and structural variation poorly.

What Genome Sequencing Adds

Whole-genome sequencing has no capture step, so coverage is more uniform and it includes introns, promoters, regulatory regions and the space between genes.

This makes it better for structural rearrangements, deep-intronic variants that affect splicing, mitochondrial DNA, and mutational-signature analysis. It generates far more data and costs more to run and store.

Use in Cancer

Research tumour studies use both; clinically, targeted panels dominate because they are cheaper, faster and easier to interpret. Whole-genome sequencing is used in some national programmes and for tumours where panels are uninformative.

Tumour mutational burden is defined from whole-exome data in its original form, and panel-based estimates are calibrated against it, which is relevant when comparing values across assays.

Use in Inherited Disease

For rare inherited conditions, whole-exome sequencing has a solid diagnostic yield, and whole-genome sequencing adds incremental diagnoses by catching structural and non-coding variants the exome misses.

Both raise the question of secondary findings in genes unrelated to the reason for testing, which laboratories handle according to consent and policy.

Interpretation Notes

Neither approach guarantees complete coverage; exome capture has gaps and even genome sequencing struggles with highly repetitive regions.

The report should state the method and average coverage, and a negative result is bounded by what was actually sequenced well.

Key Takeaways

• ·Exome sequencing deeply covers coding regions at lower cost but misses non-coding and structural variation.
• ·Genome sequencing has uniform coverage and captures structural, intronic and regulatory variants.
• ·Clinical cancer testing mostly uses targeted panels; genome sequencing is used in specific programmes.
• ·Tumour mutational burden is anchored to exome data, affecting cross-assay comparison.