I first tested my father’s Y-DNA back in 2014- and it wasn’t until a few weeks ago, five years later, that he finally received a match who shares his surname. This issue is more common than you might think- and it isn’t necessarily a warning sign of illegitimacy in the family (although that’s always a possibility to keep in mind too.)
Until this new match was received, of the three unrelated Y-DNA kits I manage, only one tester had any matches sharing his surname, although he still had dozens of matches with different surnames. The other two testers had no matches sharing their surname at all (or even anything similar).
Taking a step back, here is a brief tutorial on Y-DNA for those unfamiliar:
Y-DNA tests are only offered to genealogists through only a few testing companies- this is a different kind of test than the autosomal DNA test offered through AncestryDNA, for example. All the Y-DNA kits I manage were tested through Family Tree DNA.
Y-DNA follows the paternal line and the test can only be taken by a male.
Y-DNA is passed from father to son, so by testing my dad, I know that he received his Y-DNA from his father, who in turn, received his Y-DNA from his father, and so on back through time.
When I look at Dad’s Y-DNA match list, I see names of other men who have tested, who likely share a direct male ancestor with my dad at some point in history.
In theory and in a perfect world, we might think all Dad’s matches should have Dad’s surname (Conroy). But in reality, it’s not so simple, and here are a few reasons why:
Due to the nature of Y-DNA, Dad and a match’s Most Recent Common Ancestor might be from hundreds of years ago, possibly at a time when surnames weren’t set in stone. (Irish surnames began to be adopted in the 1300’s by the wealthier people, with many families not adopting surnames until the later 1500’s). Prior to surnames being uniformly adopted, the Irish practice of using Mac’s or O’s prior to a father’s or ancestor’s first name to create a type of surname was a common practice, meaning that surnames changed with nearly each generation.
Another possible reason for my father to have DNA matches with various surnames is that many Irish anglicized their surnames, beginning about 1550-1600. One common anglicization of Conroy is the surname King, which happens to be the surname found in highest frequency on Dad’s match list. Why Dad’s ancestors were still using the surname Conroy/Conry when they arrived in Canada in 1825, long before the resurgence of interest in reclaiming Gaelic names began, is an interesting question.
Another issue explaining why Dad had no Conroy surname matches, is that he simply didn’t have any close matches. This is definitely the issue with the third kit I manage, that still has no common surname matches. That tester has only one match at the 67 marker level, and it’s not a close one. At the 111 marker level, Dad and his surname match still have a Genetic Distance of 4 between them. Family Tree DNA estimates that they have a 99% chance of sharing a common ancestor within the last 24 generations, but only a 71% chance of sharing a common ancestor within the last 8 generations. We haven’t figured out the connection yet. Dad’s next closest match at the 111 marker level, has a Genetic Distance of 7, and is therefore probably even more distantly related. The further back the Most Recent Common Ancestor is in time, the more likely that the issues described here surrounding Irish surnames will come into play.
Family Tree DNA's TiP calculator that estimates the number of generations to the most recent common ancestor between Dad and his surname match.
Of course, there are the usual possibilities for unexpected surnames- adoption, infidelity etc. that could have occurred both in our tree and in our matches’ trees, multiple times over the decades and centuries. Put these reasons all together, and we shouldn’t be surprised to see a jumble of surnames on many men’s Y-DNA match lists.
However, as more men test, most can expect to get closer matches- likely meaning that more matches will share surnames. We can also be proactive and encourage men with our shared surname to test. We can also try to find potential testers through traditional paper genealogy or through autosomal DNA testing, and ask them to Y-DNA test, if they appear to be in the proper inheritance line to share Y-DNA with our kit. Otherwise- it’s a waiting game, but hopefully one that will pay off for us eventually to help us solve tough genealogical problems.
 Claire Santry, The Family Tree Irish Genealogy Guide, (Cincinnati, Ohio: Family Tree Books, 2017), 92.
 Patrick Woulfe, Irish Names and Surnames (Dublin, Ireland: M.H. Gill & Son, 1922), 36; digital images, Internet Archive (https://archive.org/details/irishnamessurnam00woul/page/36
: accessed 4 November 2019).
 Patrick Woulfe, Irish Names and Surnames (Dublin, Ireland: M.H. Gill & Son, 1922), 67.