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Y-STR Testing

An STR is a short tandem repeat. This is a place in your genetic code where a letter sequence is repeated. For example, AGTAAGTAAGTA is three repeats of the sequence AGTA. It is thought these sequences repeat themselves so that even if a section is lost, the genetic code is preserved. These changes are called mutations, and because there are so many places where a portion of the sequence can be added or removed, STRs have a faster mutation rate than other types of DNA.

Applications to Genealogy

When an STR value (the number of repeats) changes, this change is passed down to future generations. Y-STR testing focuses on repeats found on the Y chromosome. Only males have the Y chromosome, so these changes are carried exclusively on the male (direct paternal) line. Over time these changes build up to create a unique Y-STR signature that is unique to specific lineages. These signatures rarely go more than a few hundred years without significant changes. Y-STR tests examine a fixed set of markers known to have high variability on the human Y chromosome. They are an effective way to identify men who share a paternal ancestor within relatively recent times.

In many cultures, children inherit their surname from their fathers. As Y-DNA is also inherited from fathers, Y-DNA testing is particularly useful for surname studies.

Your Ancestral Origins

Our Y-DNA marks the path from our direct paternal ancestors in Africa to their locations in historic times. Your ancestors carried their Y-DNA line on their travels. The current geography of your line shows the path of this journey. You can learn about the basics of your line’s branch on the paternal tree from your predicted branch placement. This information comes from scientists who study the history of populations across geography and time using Y-DNA. They use both the frequencies of each branch in modern populations and samples from ancient burial sites. With these, they are able to tell us much about the story for each branch. This traces back hundreds, thousands, or even tens of thousands of years. Your branch on the tree tells you where your paternal ancestors are present today and about their likely migration paths. This is your Y-DNA haplogroup.

Levels of Testing

When you or a male family member takes a Y-STR test, FamilyTreeDNA compares your Y-STR markers to other test takers to provide a list of people who share a common direct paternal ancestor. The fast mutation rate of STRs means the common ancestor you share with these matches is likely within the past 15 generations. 

There are different levels of testing consisting of sets of anywhere from 12 to 111 STR markers. By comparing more markers, we are able to get a clearer idea of how similar your Y-STR signatures are. The more differences there are in the markers, the more generations have passed since the paternal line split for the two individuals. If you think of the matching database as a puzzle consisting of 111 pieces, the more pieces you compare means the more complete the picture becomes. 

Choosing a Y-STR Test

Depending on your objectives for testing, you may only need a few STR markers to confirm a theory or to test the waters. Sometimes a person takes a lower-level test such as a Y-37 and discovers many, many relatives. In a case like this, it may be a good idea to test additional markers. This will help you discover which relatives are the most closely related to you genealogically. Sometimes a person discovers they have a Y-STR signature that is not abundant in the database, and more markers are not needed. This may change in the future as the database grows.

Regardless of which test you decide to take when you submit a DNA sample to FamilyTreeDNA, we store your sample in our state-of-the-art lab in case you wish to order additional testing. This can be months or years after your initial test. If you order a lower-level Y-STR test, you can always upgrade to a higher-level test and only pay the difference in price between the testing levels.


Who should take the test?

  • If you were born as a biological male, you have a Y chromosome, so you can test.
  • Anyone can test a male relative like a brother, father, grandfather, uncle, or direct-line male cousin.
  • If you have already tested your paternal line, you can also recruit a tester for other lines. For example, a maternal uncle for your mother’s paternal line.
  • It is usually better to test the oldest living relative from the lineage in which you are interested. They might have a more ancestral genetic signature, and with their DNA in storage, you have the option to upgrade their test results in the future. (Just remember to ask the sample donor to make you their beneficiary.)


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