Why is Y-DNA testing so helpful for genealogy and how does it work?

+11 votes
If you want to know why Y-DNA testing is so great, please read Roberta Estes' new blog:


I hope it will encourage some of you who have only had an AncestryDNA, 23andMe, or Family Finder test to also have a Y-DNA test.  If you are female then test your male relative.

Thanks and sincerely, Peter
in The Tree House by Peter Roberts G2G6 Pilot (612k points)
edited by Peter Roberts

Peter, Did you see that the Archbishop of Canterbury, Justin Welby, just had his Y-DNA tested.  Both he and his mother were shocked.  He was born exactly 9 months after his parents marriage, and everyone thought he was a "honeymoon baby."  Turns out, his mother had a brief alcohol fueled "encounter" with Sir Winston Churchill's secretary, Sir Anthony Montague Browne before she married Gavin Welby.  The Archbishop is the son of Browne!  You can read more about it HERE.

Future learn "Genealogy. researching your family tree - University of Strathclyde"

1 Answer

+2 votes
Ok, let me play devil's advocate here (once again). Not every Y-DNA test is the same. While Y-DNA and mtDNA tests are great for a long look back into the past (to know where in the paternal and maternal phylotree you are), a STR Y-DNA test is anything but precise in the short time frame that we're usually operating in (meaning the last 300-400 years).

Surely there are people who have due to some lucky circumstances records that go way further back (mainly noble families and those that had large areas of land eg) but this is a very small minority.

Big Y and Full Y is different as it uses SNP's and is now breaking into the Genealogical Time Frame (GTF) in several projects already, meaning it provides enough depth to build very diverse trees like the famous R1b project that now has over 10000 members who contributed to it.

But anything below a 67 marker Y-DNA test (12, 25 or 37) isn't very precise in it's results. There are many examples where a perfect 37 out of 37 match turns out several markers off when upgraded to 67 or even 111 markers.

Not even speaking about cases like me, I've done a 67 marker test and I have no match, not even at 12 markers! Not even anything close (at least within the thresholds that FTDNA uses). My male line is from Asiago Italy for hundreds of years (the Basso are first mentioned in 12xx) but that remote little mountain village is now proving to be completely useless unless I get some descendants from there to do a Y-DNA test.

So yes, every DNA test has it's value (just keep in mind that they are all focusing on different problems) but a Y-DNA is less important and helpful than an autosomal DNA test IMO.
by Andreas West G2G6 Mach 6 (64.0k points)
Hello Andreas, Are you able to provide an example in WikiTree where two males (with YSearch IDs) having the same or similar surnames match 37/37 but only match 61 (or less) out of 67 markers  (or only match 101 [or less] out of 111 markers)?

Thanks and sincerely, Peter
Hi Peter,

I remember reading about those cases in the DNA genealogy list. I think it's best to place your question there as there are a couple of experts with a huge amount of experience in Y-DNA. Not sure if that mailing list has an archive to look it up.

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