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DNA Q&A: What’s the Big Y-700 Test? Should I Choose a Y-DNA Test?

By Diahan Southard Premium

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Q: What is the Big Y-700 test offered by Family Tree DNA? Do I need it?

Q: I’m trying to decide between autosomal DNA and Y-DNA for my paternal uncle. The line has been traced back to Nova Scotia for a number of generations, and I’m trying to go further back to find the original immigrant. Which test should I use?

Q: I had my nephew do the Y-DNA111 test to trace our paternal line and try to break through a brick wall. How can I understand and use the test results?

Q: I was adopted and I’m trying to prove my surname connection to a possible biological relative. I believe that I’ve found a male third cousin. Each of us is in a direct male line back to a common great-grandfather. Which Y-chromosome test(s) would be appropriate to prove the relationship?

Q: What is the Big Y-700 test offered by Family Tree DNA? Do I need it?

A: In January 2019, Family Tree DNA (FTDNA) announced the Big Y-700 test, a new upgrade to its Big Y test. As the name suggests, the Big Y test examines DNA on the Y chromosome, which only men have. You can use Y-DNA to sort out genealogical problems in your paternal line or involving surnames (since surnames follow paternal lines in most cultures). For example, Y-DNA can help you determine if two men with the same (or similar) surname share the same male common ancestor.

The Big Y-700 actually includes two tests: one that can help make more distant ancestral connections, and one that helps with more recent connections. These tests correspond to two different kinds of DNA markers, called STRs and SNPs:

  • Short tandem repeats (STRs) are repeated sections in DNA that can vary between populations and generations. This variation makes STRs ideal for determining closer relationships—perhaps within 10 generations or so. The “700” part of the test refers to the 700 STRs that are tested, an upgrade from the 500 offered by FTDNA’s earlier “Big Y-500 test.” (Family Tree DNA also offers less-expensive tests that examine 37, 67 and 111 STR markers, respectively.)
  • Single nucleotide polymorphisms (SNPs) are single changes in the DNA. Some of these SNPs have a very slow rate of change (think tens of thousands of years!), while others change much faster. This steady nature of many SNPs allows scientists and genealogists to learn about human migration and the relationships of their own distant ancestors.

Benefits of the Big Y

The Big Y really shines because of its SNP analysis and exploratory nature. Other SNP tests, like the ones used to test our autosomal DNA, are like planned tours of your chromosomes. Each of these tours examines a designated 700,000 or so stops along the chromosome. If you are traveling along chromosome 7 and see something interesting a ways off the path—too bad! You can’t stop!

But the Big Y is like a jungle safari. You have a guide, but you can explore interesting trails you come across and generally deviate from the planned course anytime you like.

This means the Big Y test will find unique Y-DNA variants that only your specific paternal line carries. Only men who share a direct paternal line with you (perhaps 10 to 20 generations) will share these SNPs with you. These SNPs help fill the gap between what the STRs can tell you (about 10 generations back) and the oral histories or genealogy you have stretching (at best, back to the 1400s or so). On average, the Big Y test will find about 70,000 SNPs on your Y chromosome that make up your Y-DNA signature.

Do I need the Big Y-700 test?

Well, that depends. The Big Y-700 test is most valuable for individuals who have solid paper trails and traditional Y-DNA testing that matches others going back at least eight generations. It will help them find connections with men who may connect to them around that 12-to-15-generation mark before surnames existed to guide us. The “700” part of the test could provide greater definition between the lines they already know are related. Many related lines have zero or just a few differences at the 111-marker level—great for determining relatedness, but terrible if you want to figure out which of four brothers was your ancestor. The Big Y-700 test could find those differences.

Q: I’m trying to decide between autosomal DNA and Y-DNA for my paternal uncle. The line has been traced back to Nova Scotia for a number of generations, and I’m trying to go further back to find the original immigrant. Which test should I use?

A: While autosomal DNA testing is valuable and has helped countless genealogists find their families, it has two glaring flaws: It’s shortsighted and it’s blurry.

To the first point, your autosomal DNA can help with only about five or six generations of your family tree. You do have autosomal DNA from your eighth-great-grandfather, but it’s in tiny pieces. Current tests can’t use such small pieces to tell if you match someone else because you share an eighth-great-grandfather, or you both just came from the same population group.

Autosomal DNA testing is blurry because it doesn’t give you a clear picture of how you’re related to someone. Based on how much DNA you share, you might be estimated as third cousins. But you also could be fourth cousins, third cousins once removed, second cousins twice removed, or another relationship that shares about the same amount of DNA. Without some legwork, you won’t even know if the match is on your paternal or maternal side.

Y-DNA, on the other hand, has both vision and relative clarity. Your uncle’s Y-DNA has been passed down basically unchanged through generations of fathers, and therefore represents a near-perfect record of his eighth-great-grandfather on his direct paternal line. (Women don’t inherit Y-DNA.) Furthermore, when you find a match in a Y-DNA database, there’s no doubt that you share a direct paternal line with that match. You might not know in which generation you connect, but you’ll have a range of a few generations to start your search.

Since you’ve already traced your ancestry back several generations, you’ll probably want to have your uncle take the Y-DNA test—so long as he’s descended through male lines from the immigrant you’re interested in. The best-case scenario is that your uncle’s Y-DNA will match someone who knows more than you do about the family’s origins. Y-DNA testing is more expensive than autosomal, but it’s also worth it. You can start with the Y-DNA 37-marker test at Family Tree DNA for $169, and if you want, upgrade to a higher level of testing later without having to submit a new sample.

A version of this article appeared in the December 2018 issue of Family Tree Magazine.

Q:  I had my nephew do the Y-DNA111 test to trace our paternal line and try to break through a brick wall. How can I understand and use the test results?

A: First of all, great job pulling that YDNA test out of your genealogical tool box. Working on a paternal-line brick wall is a great way to use this testing technology.

To start making use of your test, first evaluate the match page at Family Tree DNA <www.familytreedna.com>, which is the only major testing company currently offering Y-DNA tests. The most important column in this table is the first column, called Genetic Distance. If your nephew had taken the 37- or 67-marker test, you’d want this number to be three or fewer in order for him and his match to possibly share a recent common ancestor. At the 111-marker level, though, you can allow for up a genetic difference of up to five. Within these recommended genetic distances, you can usually assume that you and a match have a common ancestor at or before eight generations into the past.

But don’t take my word for it. You actually can see for yourself the time frame in which you should be looking for a common ancestor with your match. To see these statistical calculations, click on the orange Tip button under your match’s name on Family Tree DNA’s main match page. This will show you a statistical calculation with the likelihood that you and your match share a common ancestor within a given number of generations. For example, you’ll see that it’s 70.93 percent likely that you and your match on 65 out of 67 markers share an ancestor at or before six generations. I like to start checking the matches’ trees for the common ancestor at the generation that boasts a likelihood of at least 75 percent.

understanding y-dna test results

Your choice of the 111-marker test was ambitious, as you could’ve selected the lower 67- or even 37-marker testing option, and probably still found out what you wanted to know. But in the end, you can’t ever have too much information, and you might be glad you opted for 111 markers. Remember that these numbers of marker represent locations that are evaluated on the Y chromosome. The more markers you test, the more locations you evaluate—and the better the estimate you can receive about when you share an ancestor with a match. For example, if you match someone at exactly at the 37-marker level, you should look for your common ancestor somewhere between four and eight generations back. But if you match exactly at the 111-marker level, it is much more likely that your common ancestor will be found within four generations.

Because you’ve had this high level of testing completed, you’ll want to be sure to also look for matches at the lower levels of testing. To do that, use the dropdown menu in the Filters section of your match page. Whenever you use this dropdown menu, make sure you only look at the matches who’ve had this level of testing completed, not anything higher. In the table on the opposite page, where we’re viewing matches at the 67-marker level, you’d pay attention only to Bartholomew and Samuel, and not Inglebert and Roger. This is because the numbers in the Genetic Distance column refer only to how well they match you at the 67-marker level, and not at the 111-marker level. Inglebert might match you exactly at the 67-marker level, but have four differences from you at the 111-marker level. Always evaluate your match at the highest level of testing available.

understanding y-dna test results

The best thing to do next with your results is to join a surname project. These projects gather individuals with the same or similar surnames to collaborate on paternal line research. To find one, go up to the top menu bar, and choose Projects, then Join a Project. You’ll see a list of some suggested projects (sometimes it seems these are blindly chosen without rhyme or reason) but if you don’t see your surname on the list, scroll down and type it in the search box. One of the biggest benefits of joining a surname project is the assistance of an administrator. Often your project administrator will be able to help with understanding your Y-DNA results and how they fit in with the rest of the group.

If you’ve tried all of these ideas and come up empty-handed, try getting another descendant of your Y-DNA line tested. You want to test the most-distant relative possible. Testing second cousins or closer will usually not be as helpful as testing a third or fourth cousin. To find one, go back to your brick wall ancestor, and follow a different son’s male line down to the present until you come to a living male with the ancestor’s surname to be tested. This newly tested Y-DNA can help you verify your connection to this ancestor, reveal more matches, and give you a good Y-DNA baseline to move forward with.

From the January/February 2018 issue of Family Tree Magazine.

Q: I was adopted and I’m trying to prove my surname connection to a possible biological relative. I believe that I’ve found a male third cousin. Each of us is in a direct male line back to a common great-grandfather. Which Y-chromosome test(s) would be appropriate to prove the relationship?

A: Your situation is an ideal application of Y-DNA testing, especially since you’ve already developed a theory to test.

Y-chromosome tests come in a variety of “resolutions.” Just as higher-resolution printers provide a clearer picture, higher-resolution tests provide greater accuracy. Resolution is measured in ‘markers,’ or locations on the Y-chromosome. The more markers the test evaluates, the higher its resolution.

In your situation, a basic 10- to 15-marker test would probably be sufficient to determine whether you’re related to your suspected cousin. That’s because you’re simply looking for a haplotype match, rather than trying to estimate the number of generations back to a common ancestor. (Haplotype is the term for a set of Y-DNA test results.) But I’d suggest that you opt for a mid-range test of 23 to 25 markers. This will reduce the possibility of a false-positive match. Although it’s extremely rare for two unrelated men to match closely on even a low-resolution test, it can happen if your haplotype should prove to be a very common one. (Like surnames, some haplotypes are more common than others.) Given the personal importance of this test, I’d take the extra precaution.

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