DNA Q&A: Why to Choose the Y-DNA Test

By Diahan Southard Premium
DNA background with helix magnified – high quality render. Credit: Getty Images

Question: 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?

Answer: 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.

See what genetic testing for ancestry can do for you with The Family Tree Guide to DNA Testing and Genetic Genealogy. This book discusses how to use DNA testing in genealogy – from selecting the best test to interpreting your DNA test results and branching out your genealogical family tree.