DNA Q&A: What Is the Big Y-700 Test?

By Diahan Southard Premium
Family Tree DNA offers a variety of Y-DNA tests, including the Big Y-700 test.
Family Tree DNA offers the comprehensive Big Y-700 test, an upgraded tool for Y-DNA analysis.

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.