Y-DNA Testing: Where to Do It, Why to Do It, How Many Markers to Test - Part 2

Part 2 - Why Do a Y-DNA Test?

In my previous article we talked about which testing facility to use when deciding to undertake Y-DNA testing for genealogical purposes. Now we'll look at why it's useful, which is closely tied to the number of markers you choose to test.

As I mentioned in the first article, Y-DNA testing is a rapidly evolving science and our understanding of the results it provides is changing on a daily basis. What holds true today may hold less so (or more so) tomorrow. But let's take a stab at this in the here and now. Why should you do a Y-DNA test? What, exactly, can it do for you?

First, I believe it's easier to start with what the test can't do for you.

The testing facility I prefer, Family Tree DNA, examines specific portions of the chromosome solely for the purpose of comparison with other testers in order to identify patterns that reveal familial relationships on the direct-male line. Unlike what 23andMe purports to do, a Y-DNA test through Family Tree DNA (or Ancestry.com, for that matter) will not tell you anything about your health, or that "you are a superb dancer." As I stated in Part 1 of this series, a FTDNA Y-DNA test cannot tell you if you carry a gene for cancer - it simply does not know.

DNA testing will not do your research for you. It will not provide you with a pedigree chart back to Adam, complete with family photos and amusing anecdotes. If you want that, join Ancestry.com and browse their trees, which are only as reliable as the researchers who post them (often not very). You might get lucky and your DNA test might connect you with another researcher who can provide additional generations and supporting photos and documentation, but Family Tree DNA's results will not do your work for you. Ancestry.com's DNA test may have an edge in that respect with any ability to integrate its test results with it's paid-access family trees, but again, the trees are only as reliable as the researchers create them.

A Y-DNA test from Family Tree DNA will simply provide you with a panel of seemingly random numbers and the names and contact information of your genetic matches. The numbers represent the individual values that count the number of repetitions between selected genetic markers. That information has no inherent value until you compare it to the results of other testers. The more numbers (marker repetitions) you match with other testers (especially within the same surname), the closer your relationship with that tester is likely to be. It is up to you to work with matching testers and figure out who your common ancestor is. While Family Tree DNA and Ancestry.com both provide general overviews about your deep ancestral origins, and haplogrouping (the depth and accuracy of which, again, depend on the number of markers tested), the real value of Y-DNA testing for genealogy lies in the two basic things a test can tell you.

First, a Y-DNA test can tell you who you are not. 

A genealogist will immediately recognize the potential usefulness of this, but let me give an example.

For two decades I wondered if my Corder relatives in early Frederick County VA were related to the only other 18th-century Corder family in Virginia -- a family who lived just over the crest of the Blue Ridge in neighboring Fauquier County. These two families were literally within walking distance, so although there was no paper trail indicating a relationship between them, given their proximity and the rarity of the surname, the likelihood of a relationship seemed very high. We fully expected to match genetically, but much to the surprise of both groups, a quick 12-marker Y-DNA test produced non-matching results! To rule out any non-paternal events skewing the results (that's just what it sounds like), we secured two newly identified and distantly-related testers from each family and upgraded all tests to 25 markers. The new tests confirmed the original results. The two families definitely did not share a common ancestor on the direct male line.

Does that mean that the two families were not part of the same historical family unit? That's a possibility that can't be ruled out. Perhaps a Corder ancestor somewhere along the line took his mother's surname, but was nonetheless part of the wider Corder story. On the other hand, it's always possible that a cuckoo slipped into the nest. We just don't know. There are limits to what the DNA can tell. This is why I spoke in the first article about the complexity surrounding interpreting test results -- there are exceptions to what seem like straightforward rules. It is up to you, the genealogist, to investigate and reason out your conclusions based on a combination of what the scientific data suggests, and solid paper trail documentation. Sometimes you end up with more questions than answers. Sometimes when you hear hoof beats you have to think "zebras," not "horses" (or vice versa). But the bottom line is that in this example case, DNA showed us that we are searching for different direct-male ancestors for these two families, despite the same surname and the close proximity of the two groups.

In a more straightforward example but along the same lines, consider how we might have used a DNA test to break through a longstanding brick wall for the Burgess family of central North Carolina. After years of traditional research, no male Burgess ancestor could be identified, only a female who we had always assumed to have married a Burgess and produced three male Burgess children. A simple DNA test would have shown a mismatch with others of the Burgess surname, and just as likely would have pointed researchers to matches within other families. I say other families (plural) because in this case, even the DNA among the descendants of the three brothers would not have matched (yep, that's right - different fathers). In this case, before the advent of DNA testing, we had to do a lot more digging before we discovered a "bastardy bond" (yes, there really was such a thing) that named the father of our particular Burgess ancestor as one "Elias Swift." A DNA test had the potential to have saved us a lot of effort and shown us the correct path a lot sooner. In this case, it could have told us who we were not (Burgesses) and possibly who we were (Swifts?). If I could identify a reliable male tester from this line, I could next compare him to the genetic signature of Swift descendants to see if our lady of the alternative 19th-century lifestyle was telling the courts the truth.

In one last example, another lineage I'm working on has a long tradition that they are descended from a prolific family of the same surname in central Virginia. The central Virginia family has a number of existing tests currently on file with FTDNA that match at high marker levels, thus creating a well-established genetic signature for that group, with which we can compare our own line's results. Our line has three tests in FTDNA's lab as I write. The results of these tests will tell us once and for all whether we need to stay on this same central Virginia family's trail, or look elsewhere. A match with the family in question would delight us all and possibly help us better understand the origins of an ancestor who met a tragic fate far from home. By the same token, a non-match, while initially disappointing (or aggravating in the sense that our family history will have to be "re-written"), has the potential to shed just as much light on our elusive ancestor if not more, in another way. A match with a different established lineage could be equally helpful. We might get lucky...

If you get lucky, a Y-DNA test can tell you who you are.

Notice that I said "if you get lucky." There are no guarantees. When I submitted my original three test samples for three different surnames back in 2006, I had no instant matches. Not a single person with whom I could compare my results. A big fat zero. But as the popularity of genetic genealogy has grown, zero matches is a lot less likely (though not unheard of), and as the years have gone by, the matching tests have trickled in, each one providing new revelations as well as new mysteries.

Just as the examples above showed how DNA can help you stop wasting time chasing wild geese, let me give you an example of how a test can actually show you who you are, and hook you up with the right researchers.

First, my Brooks family line was always problematic. Brooks is a relatively common name and there were Brooks families scattered all over the eastern seaboard, many lines tracing back through centuries. It was overwhelming and demoralizing to spend hours and hours trying to sort out all of the red herrings and unwind error-laden genealogies and questionable family trees compiled by other equally frustrated researchers (some of whom had finally given up and fudged the documentation just to get 'er done). Year after year went by and individually we were getting nowhere, often laying the troublesome Brookses aside to focus on other families.

The Y-DNA test quickly established a closely-knit group of matching (and therefore proven-to-be-related) Brooks researchers who have since set about advancing our understanding of our family's origins and migration patterns. A very knowledgeable and involved project administrator for the group has encouraged us to upgrade our tests in order to track unique mutations which can be used to identify specific branches within our family cluster. This allows new high marker-level testers to compare their specific mutations and gives them a better idea of which branch their ancestor might have come from. Without the original tests and the subsequent upgrades, we'd still be flailing around, stabbing in the dark at hundreds of unrelated Brooks connections across America. Our information-sharing between members of the correct family group, and our ongoing combined efforts have allowed us to push our research back several generations. A recent 111-marker test has even identified this family's origins in Norway 4,500 years ago, an interesting little bit of trivia surrounding our ancient heritage that explains how our ancestors may have come to be in England. (A' viking we will go, a' viking we will go...)

In another example of a test telling you who you are, my Henderson family of coastal and central North Carolina had wondered for decades whether they were connected to an older group of Hendersons who had settled on the Delmarva Peninsula in the mid-1600's. There was no paper trail connecting the two families. Subsequent DNA testing of the two lines at 67-markers has indicated not only a connection, but potentially a close one. All that remains is to identify it. In the mean time, we know that at the very least, the two family branches should be looking for a common ancestor in Scotland or very early colonial America, and can combine our research efforts towards that purpose.

Hopefully these scenarios will fire your imagination and you can begin considering in what ways the benefits of a DNA test have the potential to far outweigh the costs in your own research conundrums.

In the final article in this series I'll talk about how many markers you should test, and why more is almost always better.

Important update 1/1/16: Although I already recommend the use of Family Tree DNA as the test facility of choice, a recent article on DNAExplained.com has raised serious ethical concerns in my mind about the privacy practices of Ancestry and 23andMe. Please read this before choosing to test through either of those two facilities.