View Full Version : DNA tests for genealogy, any good ?

26-11-07, 13:50
The industry is booming. Over 20 companies now offer anyone DNA tests, against only 2 or 3 in 2001. They all offer test of the Y-DNA and mtDNA (from the Y and X chromosomes) passed directly, unchanged, from our fathers (Y-DNA) and mothers (mtDNA) from generation to generation.

Only men have Y-DNA. Let's note that women have two X chromosomes, but the mtDNA is only passed by the mother. That is why women only have one mtDNA haplogroup, eventhough they have two X chromosomes.

The main reasons to take such a test are :

for Americans, to try to determine the origin of their ancestors in Europe or Africa, or to know whether they have Native American blood.

to be able to trace back distant relatives who have migrated from Europe to the Americas.

to know one's haplotype (http://en.wikipedia.org/wiki/Haplotype) or haplogroup (http://en.wikipedia.org/wiki/Haplogroup), which can help determine one's ancient ethnicity, or know about risks of genetic diseases linked to that group (see related article (http://www.eupedia.com/forum/showthread.php?t=24801)).

to (dis)prove genetic ties between two individuals (thus acting as a "paternity test").

But just how reliable and useful are these test results ?

First of all, haplogroups can only give more or less vague clues about one's ethnic origins (see related article (http://www.eupedia.com/forum/showthread.php?t=24760)). Then, one should be careful that most of the companies offering DNA test will make you pay to know your haplotype, but will ask a supplement for the SNP backbone test required to pinpoint the exact haplogroup.

As for finding relatives at the other end of the world, or simply in foreign countries where one wouldn't expect to find them, this can get a bit tricky from a scientific point of view. Some websites like Yseach (http://www.ysearch.org/) and Mitoseach (http://www.mitosearch.org/) allow people to browse through tens of thousands of DNA test results for genealogy purposes. However, finding someone with results exactly matching yours does not mean that they are necessarily related to you !

Most of the profiles available only have a limited numbers of DNA markers tested. There are over 100 markers for Y-DNA, yet most of the companies will only test 12 to 60 of them. This means that finding a perfect match for only 24 markers does not guarantee a close parental link at all.

Furthermore, even if all markers were tested, and all were a perfect match, in the case of two individuals with different surnames, living in two countries with no history of migration from one to the other, and with a genealogy proving that there respective male ancestors did live in their respective country of origins for the last few centuries, it is highly unlikely that the two individuals share a common ancestor in the last 1000 years. Two people with the same Y-DNA could very well have a common ancestor 2000 years ago. The chances of genetic mutation in 2000 years are high, but it is not impossible that they chromosome didn't change.

Or, on the contrary, we could imagine that two unrelated ancestors 2000 years ago had a quite similar Y-DNA, with only 1 or 2 different markers, and that these markers have mutated in the same way for both lineages. Again, the probability is low, but amongst hundreds of millions of individuals + their ancestors over 100 generations, the chances of such coincidences having happened at least a few times are actually quite high.

So if you are from England and find someone with the same Y-DNA as you in, say Poland, but with no known common ancestry, it is likely that there is no common ancestry. This of course complicates things for Americans in search of their origins, if they have no clue of where their ancestors came from.

Tracing your roots, really ?

DNA testing can be useful for African-Americans who want to know which part of Africa their ancestors came from. However, most of the slave descendents came from the "slave coast", in what is now Ivory Coast, Ghana, Togo, Benin and western Nigeria. Given the little number of haplogroups in Africa, the tests won't help to be more accurate.

Americans of unclear mixed descent can learn whether they have European, African or Amerindian ancestry. But tests won't tell specifically from which tribe or ethnic group the person is descended. The only ethnic groups that can be traced back with a high degree of certainty are those with quite unique haplogroup, like the Finns in Europe.

Famous DNA ?

Some companies allow you to compare your DNA to some markers of either Y-DNA or mtDNA of famous people, like Genghis Khan, Thomas Jefferson, Queen Marie-Antoinette, Queen Victoria, Czar Nicholas II, or even Prince Philip of Oldenburg, Duke of Edinburgh.

The chances of having a match are dim, even if your ancestors are from the same country of origin as theirs. Even if your results match one of theirs, the markers are so partial that it may not mean much. I would really be intereting had all the markers been available.

So why take a DNA test ?

In conclusion, the tests are mostly useful for Europeans to know whether they are in the "mainstream" of their country or region, or whether their genes are more characteristic of people from another part of Europe, or a Europe-wide minority. Are we like others ? Do we belong to some rare genetic category that make us think and feel differently from others ? It is a way of satisfying one's curiosity. It can also help us find our place in society.

It is useful to know about the potential risks of diseases, or induce a feeling of reassurance to learn that one's haplogroup has less chance of developing such or such cancer.

t can help the anthropologically minded people understand better physical differences between people in the same country, or similitudes between those of different countries.

It can be useful to link families (in the same country, or a neighbouring country) sharing a same surname but with no genealogical evidence of a common ancestor.

Geeks might also find it interesting to compare their haplogroup to that of their partner, or start working on a possible influence of sex chromosomes on personality. After all, some people try to find such relations with less scientifically compelling attributes, like blood type, or completely unscientific ones like astrology.

That is a lot of reason that I believe to be more compelling than just trying to know who our ancestors were, or trying to find by chance some genetically similar strangers somewhere in the world.

28-11-07, 13:34
Here is an article (http://freepages.genealogy.rootsweb.com/~dgarvey/DNA/hg/YCC_R1b.html) supporting that people with the same Y-DNA are not necessarily related.

Since the majority of men of European descent belong to R1b, this group has the highest risk of so called "accidental" matches - matches due to an accidental convergence of long separated R1b lines, rather than due to recent kinship. Most different surname matches among R1b's are probably of this variety. In general, the closer a haplotype is to the R1b modal haplotype, the more of these accidental matches that will be seen.

04-10-11, 20:18
i am planning soon to take the full DNA ancestry test

21-10-12, 17:34
The best thing to do,when getting your Y-dna or mtdna tested is to test it with 2 separate different companies.Or even more than 2 but at least 2,that way if your results are exactly the same then you can deduce its probably very accurate,but if there is even a small difference than you should get it tested with a third party to be extra sure.especially when you do your subclade testing.As for your autosomal dna or your full genetic ancestry I liked dna tribes.Lots of places only do basic results,how much European or Asian and African percent ancestry you have or if you have basic northern European or Southern European overall ancestry but dna tribes actually gives more specific results,so much so that most White people (Europeans) when tested end up having very very small matches with populations from Northern India and some of the Mid-East due to the distantly shared Indo-European genetic ancestry.It will tell you exactly specifically what populations in Europe you truly are genetically most similar too and its very specific and not just a broad generalization.