Whole genome vs a DNA array
23andMe, AncestryDNA and most consumer tests use a chip that measures a small, chosen part of your DNA. Whole-genome sequencing covers nearly all of it.
How a chip and whole-genome sequencing look at the same DNA
A chip checks chosen positions.
About 600,000 of your 3 billion letters, picked because they are common in the population.
The rest is estimated.
Software fills the gaps from other people's DNA. A letter rare enough to be yours alone cannot be estimated.
Sequencing measures nearly every letter.
Each position is read about 30 times, so a rare variant shows up directly. If you carry one copy, it appears in about half the reads.
What a DNA array covers
An array is a chip with probes for about 600,000 to 700,000 positions in your DNA. They are chosen because they are common and well studied. That is enough for ancestry and many common traits.
The rest is estimated, a step called imputation. It fills in common variants between the probes using other people's genomes. It cannot find a rare variant that was never on the chip.
What whole-genome sequencing adds
Whole-genome sequencing reads your whole genome directly, about 3 billion positions, each about 30 times on average. Rare changes are measured in your own DNA.
That matters because many of the variants with the biggest effect on health are rare. They include variants behind inherited conditions you could pass on to a child, and variants that change how you handle some medicines. A chip usually does not include them.
Sequencing also shows larger changes, such as missing or extra copies of a gene. That matters for CYP2D6, a gene that helps clear many common medicines. Extra or missing copies change the result. A chip measures them poorly.
Side by side
| Compared | DNA array | Whole-genome sequencing |
|---|---|---|
| How much of your DNA | About 600,000 to 700,000 chosen positions | About 3 billion positions, each read about 30 times |
| Common variants | Yes, the well-studied ones | Yes |
| Rare variants | Only the few printed on the chip | Yes, including ones almost unique to you |
| Larger changes (deletions, duplications) | Large ones only, with little detail | Yes, including smaller ones |
| Medicines (pharmacogenomics) | Common variants in some genes | The full genes, including rarer variants |
| Ancestry and traits | Yes | Yes |
Helixir offers one test: whole-genome sequencing from a cheek swab, every result checked by a scientist.
What does a DNA array miss?
An array measures only the positions printed on its chip, then estimates common variants between them. It misses most rare variants, many structural changes and much of the detail in genes that affect medicines. Estimation cannot recover a rare variant that was never measured.
Is whole-genome sequencing worth it over a DNA array?
For ancestry and common traits, an array is enough. Whole-genome sequencing is worth it when you want rare variants, carrier screening across thousands of genes and full detail on how you handle medicines, all measured directly.
Can I use my 23andMe or AncestryDNA file?
No. The whole-genome test starts from a new cheek swab, and your old file stays yours. The chip measured about 0.02% of your DNA. The new test covers about 3 billion positions.
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Your DNA stays the same all your life. Adriano De Marino, PhD, reviews every report.
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