Y-DNA clarification please

[ozdelver]

Hi,
I would like to get clarification regarding a Y-DNA test result vs an atDNA test result.

Am I correct in thinking that two men may not be a match through atDNA testing, but can still be a match using Y-DNA, ie they can have a shared common male ancestor but not share any atDNA?

From what I have read, the Y-DNA test is a completely different test, using only the Y chromosome. The atDNA test is looking at the 22 other non-sex chromosomes. Is this correct?

Any help or advice on this would be very much appreciated.

[sugarfizzle]

Since autosomal DNA is only reliable for a few generations, and Y DNA is supposedly reliable for many more generations, then it follows that two men could be Y DNA matches but not autosomal DNA matches.

Depending on what time frame you are looking at could determine which test is best for you.

Regards Margaret

[pughcd]

Hi Ozdelver,

You are correct on all points. You can match on autosomal DNA and Y-DNA (males only) independently. It depends on your research question and time-frame which test you do first.

Since FamilyTree DNA is the major player in the Y-DNA market, you may wish to watch some of the FT-DNA Webinars hosted by Elise Friedman;

https://www.familytreedna.com/learn/ftdna/webinars/

Good luck.
pughcd

[ozdelver]

Hi, and thankyou for your replies.

I needed clarification because both men have done atDNA tests and did not match each other, but each man has a sister who has also done the same test, and both women did match each other, 4th Cousin level. We were hoping the men would also match to each other, to help firm up a lead on a search for birth parents of one set of siblings' father.

I am now not so concerned that the men didn't match, and we may need to go down the path of a Y-DNA test to confirm or disprove a common male ancestor for the two men.

I will take a look at the webinars tomorrow, and see if they can throw a bit more light on the question. DNA results can be very random and confusing sometimes!
Thanks again,
Ozdelver

[AlanBoyd]

67% of English men carry the R1b Y haplotype (including me). This means that if you are English a Y test could disprove a relationship, but may well be poor evidence for a relationship. Of course you might find that both men have a rare Y haplotype — or your heritage may make a Y test somewhat more useful in this regard.

Accord to Ancestry the probability of two 4th cousins not matching with atDNA is around 30%, so not at all unusual.

[sugarfizzle]

Ozdelver, There have been several similar threads recently, questioning why 4th or 6th cousins etc do not show up as autosomal DNA matches.

If the sisters match each other, then I would think it safe to assume that the brothers are related to each other as well. That is assuming that the brothers and sisters are proven by DNA to be full brothers and sisters!

Whether a yDNA test would be worth doing as well is open to question. As AlanBoyd says, it may not prove a relationship either, though I am not up to date with yDNA testing.

I personally would stick with the sisters being matches, and work from there.

Regards Margaret

[ozdelver]

Hi AlanBoyd,
Please excuse my confusion, but I don’t understand the reference to haplogroups. My understanding re Y-DNA was that if Man A and Man B had a common ancestor (in this case a 4xg grandfather), then both men would carry the same Y-DNA, inherited down the male line to each man via two different sons of the 4xg grandfather.

Five of our family members have now done DNA tests, and after months of investigation, the resulting atDNA matches have led us to a likely paternal grandfather family line, with a prime suspect for birth father who was in the right place at the right time. That line leads to Man B via his sister, who does match some of our family members. If the predicted paternal line is correct, then my understanding is that both Man A and Man B will have the same Y-DNA inherited from their common 4xg grandfather.

Do we need to test for a Y-DNA match? I’m not sure. Is having three atDNA matches at 4th Cousin level along that paternal line to the common 4xg grandfather sufficient proof to point the finger at our suspect? He has no living descendants, and no nephews or nieces either, so no-one here that could be tested for a closer match to our family. His aunt has provided three strong matches amongst her descendants, but those matches are all shared only with matches on her female (grandmother) line, and none with the aunt’s paternal line (and therefore the paternal line of our suspect).

I think the answer will be to just be patient and wait for more matches to hopefully appear on the radar in the not-too-distant future. In the meantime, I think I will upload the DNA to FTDNA and see if we get any matches there.

Thanks for all your help and advice. DNA is such a confusing part of genealogy, I guess because it is still fairly new and this is my first foray into the science. But I do feel we can break this brick wall, given enough time.

[AlanBoyd]

Hi Ozdelver,

Yes, if man A and man B have the same ancestor in the male line then they will have the same Y chromosome. The point that I was trying to make is that if, for example, man A had a Y chromosome that corresponded to haplogroup R1b then they would match with me but that would be very weak evidence for a recent shared ancestor because so many western European men have that same Y chromosome. This is why the Y chromosome couldn’t be used to prove that someone was the father of a child for example, it would only ever be consistent with parenthood. However if the two had different Y chromosomes then that would disprove paternity. The same is true in your case–if the two men shared a Y chromosome then that would be consistent with them being related through the male line, but would not strengthen the case that they had a recent shared male ancestor.

Someone else further up the thread referred to time frames and I think that this what they were getting at – if you want to know something about your ancient heritage then the Y chromosome can tell you about that, but for your recent ancestry it can really only be used to disprove a relationship.

Hope that makes sense,

Alan