Why so many surnames on Y-DNA results?

[Jim Barrett]

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OK, this is a real newbie question!

So, in 23 matches, there were 16 different surnames. How can this be, if everyone on the list is connected through the Y-chromosome? Thanks for any enlightenment!

To answer your question we need to know how many markers were tested to give you the 23 matches.

Are you looking at 12, 25, 37, 67 or 111 marker matches?

[The_Contemplator]

If you only tested at Y12, some of these matches could be false leads. Testing higher to at least Y37 is advisable. I've seen a few kits that have one or two STR changes in the the first 12 STRs that cause them to miss their real matches.

Some STRs mutate faster so closer matches may actually differ a little more than a GD of 1 but won't show up in a Y12. As Clintonslayton has said, surnames can't really be too trusted sometimes. They have been known to have change for any number of reasons. Some of these matches could be very distant matches, with a common ancestor from thousands of years ago. As time went on, enough STRs may have remained the same between these lineages that they appear more closely related. This is why upgrading is useful. If you did test to Y37 but these matches only show up on Y12 and they have tested higher, than they are not close matches within the genealogical time frame.

[clintonslayton76]

The Y chromosome is not noted for mutational stability, but it is more stable than surname use, which is arbitrary by comparison.

Genetic distances are skewed by the number of STR markers, and are hopelessly optimistic (tending towards 0) at the lowest resolution 12-markers. As more men do higher res tests, those will be more realistic, but still estimates.

When you start seeing very high matches with high res tests and non-matching surnames, then you have to start wondering. Some surname project admins will allow JOINs with high matches regardless of surname, for study purposes. I do, with high matches who might be adoptees in two cases.

You might also get some tips from haplo admins by JOINING, and in the case of some haplos like R-m269, further SNP distinctions might be necessary for closing in on a haplogroup. I mention because R-m269 is a common Irish-Scottish haplo, as most of these names appear to be, and that might be yours.

The KILLIAN is obviously a clue, and since I do not know if your have JOINED, I find this:
https://www.familytreedna.com/public/killian_killion/
I intend no insult to your intelligence, it is better not to assume that you have JOINed, in case you have not.

[KevinKillion]

OK, this is a real newbie question!

In a Y-DNA test with known direct male-line heritage to Ireland, why are there SO MANY different surnames in the list of matches?

In this sample, there were no matches at a genetic distance of 0. But there were 23 matches with distance 1, with these surnames, and tallies for each:

Quinn /
McGee ///
Grant ////
Clinton /
O'Toole /
Killian /
Carnes ///
Collins /
McClelland /
Dougherty /
Sinclair /
Cawthon /
Ravenell /
Wade /
Thrasher /
MacKenzie /

So, in 23 matches, there were 16 different surnames. How can this be, if everyone on the list is connected through the Y-chromosome?

Thanks for any enlightenment!