By: Katy Rowe-Schurwanz

Editor’s Note: This is part two of a five-part series about what Y-DNA is, what Y-DNA can tell you, and how to apply Y-DNA results to your genealogy. Continue reading the series here:

Y-DNA has a unique inheritance pattern compared to other types of DNA. Fathers pass down their Y-DNA to their sons, with relatively few changes from generation to generation.

This means that your Y-DNA can be used to trace an unbroken line of men in your family tree going back dozens of generations—your dad, his dad, his dad, and so on—stretching so far back that ancestors’ names have been lost to time.

Overview of Y-SNPs (single nucleotide polymorphisms) and Y-STRs (short tandem repeats)

There are two options for Y-DNA testing:

  1. Y-STR testing
  2. Y-SNP testing

How Y-SNPs and Y-STRs are used in genetic genealogy.

STR stands for short tandem repeat. These are repeating sequences of the nucleotides A, C, T, and/or G (for example, CATCATCAT).

The number of repeats of a specific sequence can change over time (so CATCATCAT can become CATCATCATCAT). These changes in repeats are passed down to future generations, which creates unique Y-DNA signatures for each specific lineage.

The number of repeats is compared to determine matching with the Y-37 and Y-111 tests.

SNP stands for single nucleotide polymorphism. These are changes in the individual nucleotides; the As, Cs, Ts, and Gs. These can also change over time (A becomes T, C becomes G, etc.).

These single changes are passed down to future generations, making each lineage unique.

SNPs change at a slower rate than STRs, which makes them more stable for matching and better for determining the TMRCA between matches.

Introduction to FamilyTreeDNA Y-DNA tests: Y-37, Y-111, and Big Y-700

FamilyTreeDNA offers three levels of Y-DNA testing:


Y-37 tests the least amount of your Y chromosome. This test is really an entry level shot in the dark to see what you can discover. It’s also good for confirming if two or more men match before upgrading them to a higher level to get more granular information.


Y-111 tests all of the genealogically relevant STRs and can refine matches for a better TMRCA estimate. You may be able to confirm a specific surname with this test, and potentially even which branch of that surname if enough testers from it have results. It provides more detailed information for you and for Group Project administrators to place you in the project.

Big Y-700

Big Y-700 is the test that is going to determine who your closest matches are, provide the best TMRCA estimate, distinguish between different lines of the same surname, provide your most specific haplogroup, link your recent genealogy with ancestors who lived before the adoption of surnames, and you get lifetime analysis—your results keep improving as the database grows.

Essentially, the more of the Y chromosome that’s tested, the better the results for comparison with matches. Start with the highest level you can afford to get. You can always upgrade to a higher level.

One thing to note: Your direct paternal line matches may not have tested as high as you have. You may need to wait for them to catch up to encourage them to catch up by upgrading, or even recruit some more patrilineal cousins to test in order to reap the most benefits.

In part three, we will address how to apply Y-DNA results to your genealogy. Make sure to subscribe to our blog to receive part three straight to your inbox.

Headshot of Katy Rowe-Schurwanz - Product Manager at FamilyTreeDNA

About the Author

Katy Rowe-Schurwanz

Product Manager at FamilyTreeDNA

Katy Rowe-Schurwanz has always been interested in genealogy, inspired by her maternal grandparents, who told her stories about their family and family history when she was little. After studying anthropology and history in college, she joined FamilyTreeDNA in 2015 and became the Trainer for Customer Support. Katy created and improved training processes and was fundamental in the creation of the Big Y Specialist team. In September 2021, she became Product Manager and has focused closely on improving FamilyTreeDNA’s genetic genealogy products.