DNA tests for Genealogy
by Jason Gavin, Special Collections Librarian
DNA testing offers the modern genealogist an important and powerful tool that can provide unique information never available to previous generations of genealogists. In fact, there are so many companies offering DNA tests on today’s market, it can be somewhat daunting to know where to begin. In short, the answer to the question – “what kind of DNA test should I take?” can be answered by asking, “What kind of information are you hoping to get?” Below I’ll review some of the different types of genealogical DNA tests out there, and explain some of the pros and cons of each.
This test examines DNA found on the Y-chromosome. The Y-chromosome is one of the sex chromosomes that determine the gender of humans. Women of have an “XX” set of sex chromosomes while Men have an “XY” combination. Consequently, one drawback of the Y DNA test is that only males can take it, and it only traces a direct paternal line. It will give you information on your father’s father’s father, and so on, but no information about any females in your line, as the Y chromosome is only inherited by males. This means a Y DNA test can be especially useful for tracing surname history and origins, as surnames are also usually inherited along a direct paternal line.
Two males descended from the same male ancestor will have inherited the same DNA marker. That means that if you or a male relative and another person have the same marker 40 generations back, this test will let you know. One interesting consequent of this is what’s called the “Genghis effect”. In researching DNA dispersal through populations, it was discovered that a large proportion of the male population in Central Asia and beyond carry the same particular Y- DNA marker, meaning, they are all descended from the same single male. Further research concluded this was probably Genghis Khan, who conquered much of Asia and whose sons (who continued ruling in various parts of the continent) would have continued passing on this marker.
In addition, Y-DNA tests can provide “deep genealogical” information. Humans began migrating out of Africa beginning as early as 60,000 years ago, but they did so in waves. Often, there would be a wave of migrations to somewhere out of Africa – say the central Asia for example – and that wave would stay put for thousands of years, before a sub group would split of and travel to another area. These waves left their DNA markers in the places they traveled and settled. These markers can thus be divided into one of a number of identifiable “haplogroups”, the migrations of which can be traced by examining what percentage of a population carries a particular DNA marker.
Y-DNA PROS: Can help trace family surname
Can provide matches with other males that have the same marker, this might help solve “brick walls”, or place your father’s line at a specific place and time.
Can provide “deep” genealogical haplogroup information
CONS: Only traces direct paternal decent.
Can only be taken by males.
- Familytree DNA offers a variety of Y-DNA tests that vary in price depending on how many markers are to be tested, and will provide member matches and surname work groups as well.
- The Nation Geographic Genographic 2.0 DNA test is more expensive, but will trace the Y-DNA line as well as the Mt and autosomal tests. However, it is focused on providing haplogroup information more than more recent genealogical data.
This kind of DNA test examines mitochondrial DNA. This DNA is only inherited from your mother. Thus this test will only provide information about you direct maternal line – your Mother’s mother, and on back. Unlike the gender exclusive Y-DNA test, however, this test can be taken by both males and females. This test is useful in providing haplogroup information, but provides the maternal haplogroup rather than the paternal. Since mitochondrial DNA is always inherited directly from the mother’s line unchanged, population geneticists can trace concentrations of particular DNA markers around the globe and extrapolate migration patterns from that. Both Family Tree DNA and the Genographic project also trace Mt DNA.
Mt-DNA PROS: Can provide matches with other females that have the same marker.
Can provide “deep” genealogical haplogroup information
CONS: Only traces direct maternal decent.
Autosomal DNA tests
These are the types of DNA tests offered by popular genealogy sites like Ancestry.com and 23andMe. The big advantage of this type of test, is that it traces both the father’s and the mother’s line. The drawback is that it is only accurate to a limited number of generations. You’ll get no haplogroup information here, but companies such as Ancestry do provide an “ethnicity estimate”. By comparing your DNA markers against a sample collection from various populations around the globe, a rough estimate can be made. They can, in effect, tell you “your DNA looks like its 20% Irish, 40% German, and 20% Russian” for example. Of course, this information can only be compared from comparatively recent generations, and is not the same as tracing one’s haplogroup back thousands of years. In addition, details about the sample population against which your DNA is being compared is generally proprietary, so we don’t know how many people were sampled, or from what exact area. Another big advantage of using companies like Ancestry.com, is that your much more likely to find a match between your DNA and another Ancestry.com user, since so many people use this popular site.
PROS: Traces both paternal and maternal lineage
More useful for more recent genealogy. Primarily 6 – 8 generations back.
Popular companies like Ancestry.com and 23&Me can provide a large number users against which to compare your DNA.
In general, these tests tend to be a bit less expensive
CONS: Lacks any “deep” genealogical component – does not provide haplogroup information
Usefulness is largely determined by how many other users of this service have similar DNA to yours – thus there is no way to know how useful the test will be before you’ve taken it.
Some accessible introductions to using DNA to trace populations available at your library:
Brian Sykes: Seven Daughters of Eve
Saxons, Viking, and Celts
Spencer Wells: Deep Ancestry
The Journey of Man