Whole genome sequencing (WGS) and whole exome sequencing (WES) answer different questions at very different price points. Understanding the trade-offs helps you spend your sequencing budget where it matters most.
What each approach actually sequences
WGS sequences the entire genome — all 3 billion base pairs in humans, including coding regions, introns, regulatory elements, intergenic DNA, and mitochondrial DNA. No targeted enrichment needed.
WES sequences only the protein-coding exons (~1–2% of the human genome) using hybrid capture probes that pull down exonic fragments before sequencing. Most disease-causing variants known to date are in coding regions, which is why WES is so popular in clinical genetics.
Comparison summary
| Property | WGS | WES |
|---|---|---|
| Genome coverage | ~100% | ~1–2% (exons) |
| Typical depth | 30–60× | 100–200× |
| Detects coding variants | Yes | Yes |
| Detects non-coding variants | Yes | No |
| Detects structural variants | Yes (best) | Limited |
| Detects copy number variants | Yes (well) | Possible but harder |
| Cost | Higher | Lower |
| Storage and compute | Higher | Lower |
When WGS makes sense
- Suspected non-coding contributors to disease (regulatory variants, splicing, deep intronic mutations)
- Structural variant detection — translocations, large deletions, inversions
- Population genomics and association studies
- Cancer genomics where structural variants matter
- Research applications where cost is less constrained than completeness
When WES makes sense
- Diagnostic odyssey for suspected Mendelian disorders
- Clinical genetics where reimbursement is geared toward coding variants
- Tumor profiling for actionable mutations — most therapeutic targets are coding
- Large-cohort studies where budget per sample matters more than completeness
Hidden differences
- WES has uneven coverage. Capture efficiency varies across exons; some regions are underrepresented or missed entirely.
- WGS has more uniform coverage and better captures GC-rich regions like first exons of many genes.
- WES requires deeper sequencing (100–200×) to call low-frequency variants reliably; WGS at 30× often performs as well or better.
- Mitochondrial DNA is automatically captured at high depth in WGS; WES coverage of mtDNA depends on the kit.
Targeted alternatives
- Targeted gene panels sequence 50–500 genes at very high depth — ideal for clinical oncology
- RNA-seq identifies expressed variants and is increasingly used as a complementary diagnostic
- Long-read WGS (PacBio, ONT) is the emerging gold standard for structural variants and complex regions
WGS prices have collapsed faster than WES — the gap that made WES economically obvious has narrowed considerably. If your question is purely about coding variants in a budget-constrained study, WES still makes sense. If non-coding variation, structural variants, or future-proofing matters, WGS is the better long-term choice.
