DNA ancestry test: where you come from

We all carry in our DNA a record of our ancestors: which regions of the world they came from, the paths they traveled and how they mixed on the way to us. A DNA ancestry test reads that record. At Laboratorio Aclimu we do it with Atlas, our genomic study, and in this article we explain what it measures, how to interpret it, and what science says about where Argentines come from.

What does a DNA ancestry test measure?

Your genome is a patchwork of segments inherited from your mother and your father, who in turn inherited them from theirs. Each segment keeps small differences — variants — that are more common in some regions of the world than in others. The test reads hundreds of thousands of those positions and compares your combination with that of reference populations: groups of people whose DNA has already been studied and who represent each region.

The result comes in two parts that tell different stories:

• Composition by region: what proportion of your DNA resembles each region of the world — European, Indigenous American, sub-Saharan African, and others. It sums up all of your ancestors at once.
• The direct lineages: two specific branches of your family tree that are inherited almost without mixing and let you trace migration routes going back thousands of years.

Composition by region: how to read the percentages

The percentages are estimates, not exact measurements, and a good report has to say so. That is why in Atlas each region carries its own margin of uncertainty, and you can view the map in more detail or with more certainty, whichever you prefer. When the data allow, the report also drills down to the subregion level.

Accuracy is not the same for every region: it depends on how many reference genomes exist for each one. The reference collections for Indigenous American populations are smaller than the European ones, so that component is estimated with less precision. This is not a flaw in your sample — it is a limit of the science available today.

Maternal and paternal lineage: the haplogroups

Besides the overall composition, there are two parts of your DNA that pass from generation to generation practically unchanged:

• Mitochondrial DNA is inherited only through the maternal line: from your mother, from her mother, and so on back in time. It defines your maternal lineage.
• The Y chromosome passes only from father to son. It defines the paternal lineage, which is why it can only be read in samples that carry a Y chromosome.

Each lineage is classified into a haplogroup: a branch of humanity's great genetic tree, with a known geographic origin and migration route. A haplogroup can tell you, for example, that your maternal line descends from one of the founding lineages of the Americas — the ones that entered the continent with its first populations.

One important detail: a direct lineage describes a single ancestor per generation. Ten generations back you have more than a thousand ancestors, and each lineage follows only one of them. That is why your maternal lineage often comes from a different region than the one that dominates your overall composition — and there is no contradiction in that.

Where do Argentines come from?

Argentina's population is often said to be mostly of European origin, but genetic studies show a more mixed history. A study from the University of Buenos Aires, published in 2012, analyzed the DNA of 441 people from different regions of the country and found, on average, 65% European ancestry, 31% Indigenous American and 4% African.

The differences between regions are large. In the province of Buenos Aires average European ancestry was 76%, in the Northeast and the South 54%, and in the Northwest 33%. And one figure is surprising: among people who reported all four grandparents born in Europe, average European ancestry was 91%, not 100%. Admixture is present even in families that consider themselves entirely European.

That is why a DNA ancestry test often comes as a surprise: family stories remember the great-grandparents who crossed the ocean, but DNA also keeps the history of the ancestors who never made it into the records.

What else Atlas includes

Ancestry is one of the sections of the Atlas report. The same study also includes predispositions, carrier status for recessive diseases, pharmacogenomics — how you are likely to respond to certain medications — and nutrigenetics and fitness traits, each with its own level of evidence. We explain it in detail in our article on what a DNA genetic test can reveal, and you can explore the ancestry section of a sample report built on a real, public genome.

How it's done

The sample is a swab from the inside of your cheek: no blood, no fasting and no medical order, from the age of 18. You only have to avoid eating, drinking — not even water — smoking or brushing your teeth for the 30 minutes beforehand. It is taken at the laboratory in five minutes, or at home with a kit delivered to a pickup point near your address. The report appears in your account about 30 days after the sample reaches the laboratory, and it does not expire.

At Laboratorio Aclimu

Atlas is the genomics service of Laboratorio Aclimu (Marcelo T. de Alvear 2337, Recoleta, Buenos Aires). Genotyping and interpretation are done in our own laboratory, with more than 30 years of experience and ITAES accreditation. You book it directly at atlasgenomico.com, where you will also find the current price.

This article was reviewed by the Laboratorio Aclimu team. The information is for general guidance and does not replace a consultation with your doctor or health professional.

Frequently asked questions

What is a DNA ancestry test?

It is a DNA study that compares your genome with reference populations from different regions of the world and estimates what proportion of your DNA resembles each one. It also adds your two direct lineages: the maternal line, read in mitochondrial DNA, and the paternal line, read in the Y chromosome.

How accurate is a DNA ancestry test?

It depends on the region. The percentages are estimates, which is why in Atlas each region carries its own margin of uncertainty. Populations with many reference genomes are estimated more accurately; Indigenous American populations have smaller reference collections, so that component is estimated with less precision.

Why doesn't my maternal lineage match my overall composition?

Because it follows only one branch of your family tree. Ten generations back you have more than a thousand ancestors, and the maternal lineage describes just one per generation: your mother's mother, and so on back in time. That branch often comes from a different region than the one that dominates your overall composition.

Can women learn their paternal lineage?

Not directly. The Y chromosome passes only from father to son, so it can be read only in samples that carry it. A woman still receives her complete composition by region and her maternal lineage.

Can it be used to find relatives?

Atlas does not compare your DNA with other people's: it reads your own genome to tell you where it comes from and what you inherited. It is not a relative-matching service.

References

1. Avena S, et al. Heterogeneity in genetic admixture across different regions of Argentina. PLoS One. 2012;7(4):e34695. Available at: pubmed.ncbi.nlm.nih.gov
2. MedlinePlus Genetics, U.S. National Library of Medicine (NIH). What is genetic ancestry testing? Available at: medlineplus.gov
3. National Human Genome Research Institute. Mitochondrial DNA. Genetics glossary. Available at: genome.gov
4. National Human Genome Research Institute. Y chromosome. Genetics glossary. Available at: genome.gov