Y-DNA STR Testing - Zero Matches?

Question

Back in early 2010, I did a Y-12 test on my second cousin via the Genographic Project. Soon thereafter, I transferred the results over to FTDNA and he had zero matches at the Y-12 level.

Now, all these years later, I finally had a chance to test his father (my first cousin, once removed). For his Father, I did a Y-111 test and a Big-Y. The Father has plenty of Big-Y matches, but for his Y-STR, he only has one match and it's at the Y-12 level: his own son who I tested in 2010!

What is the significance of such a staggering lack of STR matches? What does that mean in simple terms that I can explain to them?

For what it's worth, I also did a Family Finder test on the Father and there are a respectable number of matches, just as there are for his Big-Y. It's only the Y-STR matches which are remarkably vacant.

Answer 1

Y-chromosome STR tests measure particular aspects of the DNA (tandem repeats) which happen to change at a faster rate than most other forms of DNA change. Each STR site ("DYS" locus) tends to have an average chance of about 0.2% of mutating in each generation.^1,2 When you look at many such sites, the combination tends to diverge within a few generations.

Comparing the Y-STR results of two males does not give a simple match/no-match result. A man and his son or grandson might not have exactly the same measured numbers at each STR site, since a small number of the sites might have changed in the intervening generations. This table at FtDNA provides a guide to interpreting the number of differences for Y-111 tests. It shows that 0 to 5 differences indicate related people, 6-7 probably related, 8-10 only possibly related, and over 10 being unrelated in a genealogical timeframe.

So, if no STR matches means no one was found with exact matches at all 111 sites, that itself doesn't mean too much since just one or two generations might have a mutation at one of the many sites. At the other extreme, if there are no matches with 10 or fewer STR differences, then it means that nobody who is related through male-only lines in the past 400 or 500 years has been tested and had their data recorded in the database.

Answer 2

The match list is very limited to persons who are at distance of 10 steps from you at Y111... Some mutations may be rare, but others can happen between generations simultaneously in multiple places. So the best way is to :

1. Find out predicted and actual haplogroup (using SNP testing)

2. Begin to participate in corresponding Y-DNA or surname project in FTDNA; The projects have great comparisons tables of Y-STRs of their participants.

3. Try to use great search services like ysearch.org and semargl.me They will show as much matches as possible on distance selected by you and not limited to stupid numbers.