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Ancestral DNA tests: what should I know before I start?

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Last update November 2016


Who are we? Where do we come from? These are questions that everybody ask at one point or another. All of us learn about our country's history at school. But history has its limits. It won't tell us what makes each of us different from each others.

With the help of science, we can now determine the ancient ethnic origins of one's patrilineal ancestors, by testing the DNA of the paternally inherited Y-chromosome (known as Y-DNA for short).

History books rarely dig into personal genealogies, except for royalty. Even for royalties, non-paternity events have been known to happen. Genetic tests have already revealed that Napoleon III did not carry the same paternal lineage as his paternal uncle Napoleon I, and was apparently born out of an illicit liaison.

How can we trace our ancestry with DNA?

We have 23 pairs of chromosomes. The last pair is X-Y for men, and X-X for women. The Y chromosome is the only part of the DNA that does not recombine in children. This is because the chromosomes X and Y are of different length, and cannot merge with each others. A man therefore has the exact same Y chromosome as his father, paternal grand-father, and so on. He also inherits a blended recombination of his mother's two X-chromosomes. A woman, on the other hand, inherits one X-chromosome from each parent, which then recombine together, like all the other pairs of chromosomes.

Any man will have the same Y-DNA has his father, brothers, sons, paternal grand-father, etc. This is why all men descending from a same patrilineal ancestor (and therefore having the same surname) share the same Y-DNA.

The Y chromosome is a sequence of 59 million characters. A small number of mutations occurs every generation and are inherited by all subsequent male descendants. By looking at those unique mutations, known as SNPs (short for Single-Nucleotide Polymorphisms), it is possible to retrace one's ancestry.

Population geneticists have classified tens of thousands of Y-DNA mutations commonly found among humans around the world and have rebuilt the genealogical tree of humanity. Human beings experienced severe population bottlenecks during the Last Glacial Maximum (aka LGM, c. 19,000 to 26,000 years ago), particularly in Europe, Central Asia and North Asia. Many lineages became extinguished during that period. When the population started growing again, men descending from the same tribe carried the same long series of mutations on their Y chromosome, which their last common paternal ancestor had accumulated for several millennia before the population bottleneck occured. Geneticists chose those nodes of sometimes over 100 accumulated common SNP's to define the world's major prehistoric tribes, which they called haplogroups. In other words, people sharing the series of identical unique mutations belong to the same haplogroup, and descend from the same ancestor. The chart below shows when the main haplogroups found in Europe and the Middle East evolved.

After the Ice Age, humans recolonised Europe from LGM refugia. Other tribes moved into Europe from Anatolia and Central Asia. Agriculture was invented in the Fertile Crescent and Neolithic farmers spread in all directions, mixing with the Mesolithic hunter-gatherers that were living in Europe and other regions at the time. In the Bronze Age, Indo-European speakers developed the world's first bronze weapons and started rising horses. They conquered most of Europe, Central Asia and South Asia. Each of these migrations spread new genes and new Y-DNA lineages, about which you can learn in detail here, with explanations on the ancient ethnicities linked to each group.. You can easily compare the Y-DNA frequencies by country and region and visualise the distribution maps for each haplogroup and their principal subclades.

What are the risks of a Y-DNA test?

None. Y-DNA represents less than 1% of the whole DNA. Because Y-DNA is shared by all male family members sharing a same surname, it cannot be used to identify individuals. Y-DNA only determines if a person is male or female. It does not carry much medical information, except possibly for infertility. Tests for ancestry purposes only use a small fraction of the Y-DNA, and cannot even be used to determine infertility.

How can I test my DNA?

DNA testing is very easy. You just need to order a test kit from a testing company, rub a buccal swab into your mouth (or spit into a small container, depending on the company), and send it back by post. Results typically take from 4 to 6 weeks once the lab has received your sample.

Which test shall I choose?

The cheapest and most informative ancestry DNA tests are 23andMe, Geno 2.0, Chromo 2.0 and LivingDNA. It will not only give you your exact Y-DNA haplogroup with more precision than a Y-STR test like the one sold by FTDNA, but it will also give you your mtDNA haplogroup (most often the deepest subclade possible), and autosomal data that can be used to calculate your personal autosomal admixture using one of numerous custom calculators. Each company will also compare the percentage of similarity between your genome and those of individuals from other countries, although their accuracy still needs to be improved. 23andMe also offers the option to get health related information, including genetic traits and for disease risks.

Beware that tests like AncestryDNA and FTDNA's FamilyFinder will only give you your autosomal results, not your Y-DNA and mtDNA haplogroups. They are mostly aimed at people trying to find/compare relatives within a few generations or to estimate the percentage of autosomal ancestry inherited from relatively recent ancestry (and therefore relatively useless for Europeans or people with a good paper genealogy).

Here is a quick comparison of the DNA testing services offered (as of November 2016).

Company Autosomal SNP's Y-DNA SNP's mtDNA SNP's Price (USA/EU/UK)
23andMe 577,382 2,329 3,154 99~199$/169€/149£
Geno 2.0 700,000 ~20,000 ~4,000 180$
Chrono 2.0 290,169 14,497 3,142 345$/285€/240£
LivingDNA 650,000 20,000 4,500 159$/159€/120£
FamilyFinder 690,000 none none 79$
AncestryDNA 682,549 885 none 99$/99€/79£

What are surname projects?

Family Tree DNA (FTDNA) has thousands of Surname DNA Projects where people can compare their Y-chromosomal DNA with other members with the same or a similar surname and try to determine which members are related and how many generations elapsed since their last common ancestor. To join such a project, you will need to take a specialized STR (Short Tandem Repeats) test, which is different from the SNP test of 23andMe and Geno 2.0. Surname projects are based on the Y-chromosome, since surnames are inherited from one's father and therefore follow the Y-chromosomal lineage. Only men can take the test. The advantage is that these STR tests are more accurate to estimate recent shared ancestry than basic SNP tests. It is consequently the favoured method for genetic genealogy, especially for people who want to verify their family tree with distant cousins, or ascertain common descent between individuals who share the same surname but lack a paper trail to connect them.

Your test will only tell you about your agnatic (patrilineal) line, but nothing prevents you to ask other male family members having a different surname than yours to take a test too. To know your mother's agnatic line, you should test either her father (if still alive), one of her brothers, or one of her paternal uncle. The same can be done with your grandmother's agnatic lines, by testing one of her brothers, or male children of a brother. Relatives can even be distant cousins, as long as they are male and have the same surname.


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