Do Ancestry DNA Tests Work?

Nowadays many people resort to consulting DNA testing companies to determine where their ancestors have come from. For individuals from an uncertain or mixed background, this is especially intriguing, as proportions of inherited DNA from grandparents or generations further back can vary considerably.

Y-DNA, mtDNA and Autosomal DNA

Most DNA tests regarding ancestry provide either one or all three of the following: The Y-DNA Haplogroup, the mtDNA-Haplogroup and an estimate of autosomal DNA. The Y-DNA haplogroup is only inherited by male offspring, as a Y-Chromosome is necessary. People with the same haplogroup share a common ancestor, usually a couple of millennia back. The same is true for mtDNA, which is passed on by a mother to all her children, regardless of gender.

In regards to determining where your ancestors eventually came from the Y-DNA haplogroup is especially useful, as males traditionally stayed in their communities and took brides from other settlements, villages or tribes, making mtDNA-Haplogroups, on the other hand, less reliable for determining the exact origin of the specific line of descent. As a result Y-DNA haplogroups usually peak in certain areas, whilst mtDNA is more spread out over greater distances without clear boundaries or concentrations. This is not to say that Y-DNA haplogroups have exceptionally clearly defined areas of distribution, but more so than mtDNA-haplogroups. So whilst one can trace one’s ancestry back more reliably with the respective Y-DNA haplogroup it doesn’t give much information about what DNA one’s genome is made of and neither does the mtDNA-haplogroup. To find out about the actual composition of one’s genome autosomal DNA needs to be taken into consideration.

By Maulucioni – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=21925662

Example of the distribution of the Y-Haplogroup R1b, western Europe’s most commonly found haplogroup.

By Vanesa Álvarez-Iglesias , Ana Mosquera-Miguel , Maria Cerezo, Beatriz Quintáns, Maria Teresa Zarrabeitia, Ivon Cuscó, Maria Victoria Lareu, Óscar García, Luis Pérez-Jurado, Ángel Carracedo, Antonio Salas – Álvarez-Iglesias V, Mosquera-Miguel A, Cerezo M, Quintáns B, Zarrabeitia MT, Cuscó I, et al. (2009) New Population and Phylogenetic Features of the Internal Variation within Mitochondrial DNA Macro-Haplogroup R0. PLoS ONE 4(4): e5112. doi:10.1371/journal.pone.0005112 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0005112, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=65242424

Distribution of mtDNA-Haplogroup H2a in contrast. Shows the relatively constand widespread distribution f mtDNA-Haplogroups.

Autosomal DNA tests analyse an individual’s entire genome instead of just focusing on the small parts which are the Y-Chromosome and the mtDNA and then attempt to assign certain portions (or the entire genome in case of a completely unmixed individual) to certain populations, which are most commonly defined by popular ethno-linguistic groupings like nations. So, for example, a company would define someone as 40% Asian, 40% European and 20% African and then give estimates on subregions such as 20% Northwest-European, which somtimes is further divided into nationas and subregions. Whilst these estimates are certainly entertaining and for the most part to be taken seriously they remain estimates which will become more accurate over time. Different companies have different databases and so their population estimates for an individuals autosaml DNA will differ, even if the postulated regions are the same. Apart from that, the regions themselves have to be taken with a grain of sand if they’re defined based on a specific nation as most nations consist of multiple ethnicities, which – in most cases – also changed over time.

And this brings me to the point of the reliability of finding out one’s ancestry in the distant past. As everyone should be aware, you inhertit DNA from your parents, grand-parents, great-grand-parents and so on, but with every generation back you’re less similar to your ancestors. Because of this, most ancestry tests can only provide more or less accurate insight for 10 or so generations, so about 300 years. If a user is more interested in their roots before this time it gets increasingly harder to estimate and compare one’s ethnicity and not many companies offer deeper insights. And even if they do so, it the accuracy of the results remains questionable.

An example of inheritance.

To conclude, Ancestry DNA tests certainly can give you an insight in regards to where your ancestors have come from and are a valuable source but should never be taken as a guarantee for your ethnic background, especially if you’re trying to find about your early origins. It can, however give you an estimate based on modern science and a starting point for further research, supported by historical records about your own family history as well as reports about migration events that might’ve affected your ancestors in the past.


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