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

By Diahan Southard

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.