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My maternal cousin recently took a Y-DNA test to help with research on my mother's family line. The results are back and he is in haplogroup R-M269. He has 347 matches at 37 markers.

I took a test several years ago and am in haplogroup I-M253, and currently have only 8 matches at 37 markers.

I know that it's a bit of luck of the draw as to how many matches one has, but this is an enormous difference, 8 versus 347. In both cases our paternal ancestors come from similar areas of England. I am assuming my cousin has many more matches because he is in a common haplogroup.

But then this raises the question, are those many matches likely as accurate, in terms of likelihood of sharing a common ancestor? For instance, we both have several matches at 35/37 markers. According to FTDNA's TiP report they estimate the common ancestor c.1650 (range 1250-1850) in both cases. Because of the large number of matches, is there a lower chance that my cousin's matches are related on a genealogical timeframe, if at all?

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  • He is lucky I am in the same haplogroup and have no matches at all at 37 markers. FTDNA has a much smaller pool of test results than Ancestry so that may be the reason for the large difference.
    – Colin
    May 1, 2023 at 7:04
  • @Colin Interesting, thanks. So I guess that means that my assumption that a common haplogroup means more matches is incorrect. When you say you have no matches do you mean no exact matches, or really no matches at all within a few steps?
    – Harry V.
    May 1, 2023 at 15:57
  • I have 135 matches at 25 markers but none at all at 37 markers.
    – Colin
    May 2, 2023 at 6:20
  • How many of your matches are at distance zero or 1, or match your surname? Those are really the only ones that matter. Everything else is pretty much noise.
    – cleaverkin
    May 2, 2023 at 23:35
  • @cleaverkin My cousin has no exact matches, 2 matches at 1 step, 16 matches at 2 steps. There is an illegitimacy in the line about 6 generations back, and one of those 2-step matches has the same surname of the suspected father of the illegitimate birth. Though proving the link will probably be impossible without a closer match. I think 2 step matches can be useful, with my own kit I have a match who is 2 steps at 37 markers (7 steps at 111 markers), but shares a similar (but distinct) surname to me - which I think links the surnames earlier than any paper records could.
    – Harry V.
    May 3, 2023 at 4:52

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With y-DNA, unless you get a near-perfect match at 37 markers (distance 0 or 1), it's unlikely you'll find a common ancestor in genealogical time. The total number of matches isn't nearly so significant as the number with low distance, and whether they share your surname. A 37 marker match at distance 1 or 2 with a different surname might indicate NPE in one line or the other, or it may indicate that the common ancestor predates the use of surnames.

I'm also I-M253, the estimated origin of which has been revised several times, originally thought to have arisen abt. 10,000 years ago, but the most recent estimate is abt. 3200-5000 years ago. At that point, the haplogroup spread from northern Europe into Scandinavia, and later back to the British Isles, presumably via Viking invasions. It's less common in the British Isles than R-M269 (abt. 10% vs. almost 90%), so it's likely to see fewer matches among testers with British Isle roots than someone with R-M269 would see. Haplogroup R-M269 spread westward through southern Europe to the British Isles (over the same period that I-M253 was spreading northward), accounting for the vast majority of the male population there.

With higher-marker tests, you can pinpoint more accurately when your line diverged from someone else's. There have been published accounts of Big-Y tests being used to trace contemporary families back to the ancient clans of Scotland, noting at what point in genealogical time each of the contemporary families had divergent mutations. Such exercises (obviously) involve quite a lot of samples.

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