Whole-Genome vs Whole-Exome Sequencing: What Each Covers and When to Use Them

The 1-minute summary

• Whole-genome sequencing (WGS) reads almost the entire genome (~3 billion base pairs), covering both genes and the regions between them.
• Whole-exome sequencing (WES) targets only the exome — the protein-coding portion — which is just about 1-2% of the genome, yet contains a high share of known disease-causing variants.
• WES is cheaper and simpler to analyze; WGS costs more but also covers introns, regulatory regions, and structural variation more completely.
• The right choice depends on the clinical question, budget, and the type of variant you are hunting for. Neither is universally "better."
• Both are discovery tools, not verdicts. Results should always be interpreted together with a clinician or genetic counselor.

Hello, I am a physician who works with genetic data, and one question comes up again and again: "If I want a detailed DNA test, should I just sequence the whole genome, or is part of it enough?" There is no one-size-fits-all answer, because whole-genome and whole-exome sequencing were designed to answer different questions. In this article I will walk through what each technique actually reads, how they differ on cost and depth, and when one is the better fit.

What is the exome, and why do 1-2% matter so much?

The human genome contains roughly 3 billion base pairs, but the parts that are actually "translated into protein" are the exons, which together make up the exome — only about 1-2% of the whole genome. The rest is introns and intergenic regions that regulate genes or whose function is not yet fully understood.

The reason the exome matters far beyond its size is that most of the currently known Mendelian disease-causing variants fall within protein-coding regions. So reading the exome alone still captures a high proportion of clinically interpretable variants, while using far less data.

WGS and WES read "different things"

The core difference is the scope of what gets read.

• WES uses a "capture" step to pull out only the exon regions for sequencing. It sees variants in protein-coding genes well, but misses (or under-covers) deep intronic regions and regulatory elements, and it typically detects large structural variation less reliably.
• WGS reads the whole genome without targeting specific regions, so it covers exons, introns, and regulatory regions, and detects copy-number variants and structural variants better. Its read distribution also tends to be more uniform because there is no bias from a capture step.

Put simply, WES is like reading only the "key chapters" of a book, while WGS reads the whole thing — footnotes and the gaps between chapters included.

Cost, read depth, and data volume

Cost and coverage are often mixed up, so let me separate them clearly.

• Cost per test: WES is cheaper because it reads far less data. Although WGS prices have fallen steadily over recent years, WGS is generally still more expensive than WES per sample.
• Depth (coverage): Because WES focuses on a narrow region, it often reads the exon at high depth (e.g., 100x or more) at an affordable cost, whereas WGS usually reads at moderate depth across the whole genome (e.g., around 30x). Higher depth helps confirm variants and improves detection of mosaicism.
• Data volume and analysis: WGS produces many times more data, requiring more storage, compute, and analysis time. Interpreting variants outside the coding region is also harder, because the knowledge base is still limited.

When to use which

In practice, the choice depends on the question you want answered.

1. Suspected Mendelian disease with a likely cause in a coding gene: WES is often the cost-effective first choice, especially with a limited budget or a focus on known disease genes.
2. Negative WES but high suspicion, or a suspected cause outside coding regions / a structural variant: WGS helps capture what WES misses, such as deep intronic or regulatory variants and structural variants.
3. Population research and discovery of new associations: WGS gives a complete picture of variation, suited to studies where you do not yet know where the answer hides — including studies of regional genetic diversity, such as the genetics of Southeast Asian populations we care about.

Note that many ancestry or direct-to-consumer tests use a different class of technology (such as SNP genotyping arrays), which read only predefined positions rather than sequencing the entire exome or genome. If that interests you, see our article on ancestry DNA analysis.

Limitations to understand before deciding

What the science does not yet say is something I want to emphasize.

• Neither WGS nor WES reads the genome 100%. Some regions remain hard to read — for example, highly repetitive or GC-rich stretches that current short-read technology does not cover completely.
• Finding a variant does not always mean knowing what it means. Many variants are still classified as variants of uncertain significance (VUS) that cannot yet be interpreted clearly.
• A result is only one piece of information, not a life sentence. Carrying a risk variant usually means a small, modifiable increase in risk shaped by environment — not that disease is certain.
• Deciding to test and interpreting the results should be done together with a clinician or genetic counselor, so the tool matches the question and the results are read appropriately.

References

1. National Human Genome Research Institute. Whole Exome Sequencing / Whole Genome Sequencing. genome.gov
2. MedlinePlus (NIH). What are whole exome sequencing and whole genome sequencing?. medlineplus.gov
3. Belkadi A, et al. Whole-genome sequencing is more powerful than whole-exome sequencing for detecting exome variants. PNAS. 2015. pnas.org
4. Richards S, et al. Standards and guidelines for the interpretation of sequence variants (ACMG/AMP). Genetics in Medicine. 2015. ncbi.nlm.nih.gov