Will y-DNA plus au-DNA indicate cousin distance

+4 votes
Following up my question "can y-37 and or y-111 determine cousin distance", it occurred to me that both I and my y-37 matches had an au-DNA test at the same time (the Family Tree y+au test). The au-DNA test has bought up one male who I know is a 2nd cousin, as are several female matches in the 1-3 cousin range. Two more ladies are in the 3-5 cousin range, relationship unknown, but one (ladyA) of them has a close male relative (manB) matching me at y-37. There is also a second y-37 match, all three of us having a genetic distance of 2. All the men are in the right surname group, but will presumably will need a higher level of y-DNA test to confirm a genealogical link.

However, they also had an au-DNA test, so my question is; do Family Tree compare us for both Y and au DNA matches ?. If they do not, why not ?, and how can y-matching males compare their au-DNA ?. au-DNA matches tend to be suspect at the 4-5 cousin level, but if a y-37 match also showed a 4-5 cousin au-DNA match, does it lend strong support to both a genealogical link and to cousin distance ?. If it does, what about when the au-DNA cousin distance is even more remote for y-37 or higher matches ?.
in The Tree House by Alan Upritchard G2G3 (3.7k points)
edited by Alan Upritchard

1 Answer

+4 votes
FTDNA returns your autosomal matches in Family Finder and your Y-DNA matches in the Y-DNA interface.  The two interfaces do not interact in any way.

The situation you describe of having a match at 35/37 markers who does not appear as an autosomal match in Family Finder is not at all uncommon.  A 35/37 marker match could easily be 10 or so generations in the past, which is far beyond the consistent reach of autosomal DNA testing.
by Ray Jones G2G6 Pilot (155k points)

Yep. What Ray said. A decent autosomal match with a Y-STR match may be meaningful, but you have to do all the same legwork with detailed autosomal triangulations in order to draw that conclusion. In other words, there can be no assumption, even with the same surname (and certainly not with a common surname; I know a little about that), that the autosome segments are reflecting the patrilineal lineage.

The new Big Y-500--results to start coming in soon--might take us a step closer to cousinship prediction, but I rather doubt even that will be enough detail to do more than place a closer percentage of probability of distance to MRCA in terms of generations. Biological brothers might well not match exactly, so even then--with 450 Y-STRs and all known Y-SNPs tested--an MRCA predicted distance of one generation, probably even two generations, will never be 100%.

I've used the imperfect simile before that autosomal DNA is like a very wide, broad net that is perfect for fishing in the shallows, near the shore of a lake. Y-DNA (and mtDNA, though of slightly lesser genealogical value) is like a small but weighted net that can be dropped down in the deep center of the lake. They can both be effective at catching fish, but they catch different kinds of fish in different ways. Using them together is extremely beneficial, but you can't catch the fleet fish teaming near shore with the small, weighted net designed to get the deep-water fish.

You can form an hypothesis that an autosomal DNA match that is also a Y-STR 37-marker match with a GD of two aligns with descent on the patrilineal line, but you then have to consider all the possible pathways of those autosomal segments and build triangulation groups with multiple testers to validate that the autosomes and the Y-chromosome really do converge. There's really no apples-to-apples comparison between the two type of tests, which is why FTDNA can make no assumptions about any linkage between Family Finder results and yDNA results.

Thanks Ray and Edison for your very useful comments. I have edited my initial question to identify 'ladyA' and 'manB'. LadyA is confident her father and manB are cousins. On FT-DNA I can't view the auDNA match between ladyA and manB, but assume it must be 3-4 cousin or closer.

LadyA has an auDNA match with me on ANCESTRY as a 'high' probability of 4-6 cousin. We have also both tested on FT-DNA where the match shows as even closer; 2-4 cousin. Why are they different ?.

In FT-DNA, ManB and I match at y-37. Would higher levels of y-testing improve confidence that we are related ?. We also match auDNA as'2-4 cousin, probably 3rd'.

From my family tree, I know manB can't be a 2-3 cousin, and is probably not a 4 cousin as my GG grandfather appears to have no brothers. Given this information, how confident can we be that we are related and that the indicated cousin distance is either probable or possible ?.

Part 1 <cough, cough>

Yeah. I know. I am officially the G2G Word-Count Scofflaw. Sometimes I just can't help it. I'm all about sharing information. To ignore me, the PgDn button is your friend.  :-)

I think the challenge you face, Alan, is that the devil is in the details.  ;-)  Unfortunately, AncestryDNA simply doesn't provide enough detail to make any (well, very many) but process-of-elimination judgments. All we get are their assumptions about cousinship distance plus the total cMs shared across however many segments. We can't plug that into DNA Painter or a spreadsheet or anything else to start analyzing where those matching segments likely came from.

I realize I'm gonna be doing some DNA 101 stuff in this post, so I don't want you to think I'm being patronizing; I don't know how much you've dabbled in this stuff yet and I don't want to skip something that may be useful.

When dealing with a combination of yDNA and autosomal DNA results, the atDNA analysis typically needs to come first. This is also the pathway for women to be able to use yDNA in their genealogical research: they can't contribute yDNA to test, so they need to establish the evidence linking them in proper association to a male who has taken a yDNA test.

Let's start with who--as I read things--is your best candidate: "ManB." If I'm correct, he's a Y-STR match with you at a genetic distance of 2 at 37 markers. You do share a common male ancestor. But at this point you can't know if that was your great-grandfather or a man born 12 generations ago. Unlikely, though, to be more than 10 generations. The Y-chromosome is really good at accurately determining patrilineal ancestry, and in diving back many generations with that accuracy. Not so good up close and personal. For example, I have a known 3C I'm one GD from, and a known 4C1R with whom I'm an exact match at 37 markers. However...

It sounds like both of you tested at FTDNA, yDNA and autosomal DNA. If he is also being displayed as an autosomal DNA match, the first things I would do are, A) get the detail from that atDNA match in FTDNA, and B) try to contact ManB for info about his genealogy. I'm sure you know this, but to get the match detail, from your profile go to his listing as a match. Click on the checkbox to the left of his name, then click on "Chromosome Browser." You get a nice graphic display...attractive but not much use by itself. If you hover your mouse over the segments where you match (usually shown on most browsers as a gold or orange color) you can see the details. Hard to copy them down from there, so click on "View this data in a table." You actually get more detail than you want. I personally would ignore anything below 10cM, but you can copy everything in the table and paste it elsewhere, or click on "Download to Excel" to save it as a .CSV file.

Now, there are no guarantees that the matching segments you see come only from your paternal line, even though you know you and he share a male ancestor. In fact, you can't even known that the matching segments come from your paternal line at all. That's one thing that makes autosomal DNA trickier to deal with than some folks realize. That said, what you do have is a reasonable hypothesis that those segments do come from your paternal line, so now you have to go about testing it.

Some people want "sciencey" DNA to give them quick answers about the unknown, but the truth is ya gotta put in the hard yards to identify the known first: baselines and benchmarks need to be established. There are a lot of nifty tools to help with this now. One I mentioned already is DNA Painter; another I recently bought but have only had minimal time playing with is called Charting Companion, in particular its "DNA Matrix" feature. Or you can just track everything in a spreadsheet.

The deal is that, as you've shown you know by your question, one data point does not a series make. And yDNA and autosomal DNA are apples and oranges...until you have the data confirmation that links them. First step is to create a database (even a free Google sheet works fine) with your known matches, starting from the closest--excluding parents and full siblings: too much relatedness there. If you have a good paper-trail on the individuals, then they're "known." In there needs to be detailed segment information, so--unfortunately as always--AncestryDNA data are out of the picture. Total shared centiMorgans isn't enough; you have to know the chromosome numbers, the segment sizes in cMs, and the positions as starting and ending base-pair numbers. The "known" part means that you should be able to understand where the matching segments to you are likely to have come from. Layer 1, you separate your father's and your mother's lines; layer 2 and you can start determining which set of the grandparents; layer 3 and you've got a framework for which specific grandparent because you've now determined which set of g-grandparents, and so on. 

An aside here. If using GEDmatch, which I do recommend, I suggest starting off running their "Are my parents related?" tool. Sounds odd, and maybe even a little insulting. But what it does is look at what's called ROH, runs of homozygosity: contiguous stretches of chromosomes where the two nucleotide values are the same, e.g., A-A, C-C. This is an indication of pedigree collapse; the greater the amount of ROH, the more recent the "collapse." Every family tree has it somewhere--actually in multiple places--but how prevalent it is in your own data becomes a factor in how you evaluate and weigh the size of shared segments.

Part 2

Once you construct your baseline data, it becomes much easier and more accurate to form hypotheses about where new matches fit. A somewhat extreme example of what I mean by "hard yards." Well-known genetic genealogist Jim Bartlett is often pointed to as a justification for using small segments in atDNA triangulation research. What folks overlook is that Jim never takes a 7cM segment at face value and assumes it matches anything...or is even a valid segment. Jim wrote just today:

"I use a Triangulated Group (TG) to mean a method of checking shared segments to see if they significantly overlap each other and match each other. I have grouped over 10,000 such shared segments this way -- into 385 TGs. This is a mechanical process."

Nobody needs to have identified 385 triangulation groups to get started with this stuff (whew), but that's why Jim says he can confidently work with 7cM segments: if one turns out not to be valid, it's just a rounding error because the rest of the TG has 10 or 20 other individuals with segments validating the TG. Does, though, illustrate what I mean about building up baseline data on the "knowns" before tackling the "unknowns."

If you have identified, with the needed detail, several known cousins that come from your father's side of the family and ManB's segments overlap some of them, and don't overlap cousins from your mother's side, you've upped the odds from "hypothesis" to "probable" that the Y-STR and autosomal matches line up correctly, and the atDNA results should give you a decent range in which to guess at the degree of cousinship along your paternal line.

But that still leaves LadyA. Trying to start your analysis with her and back-into ManB isn't going to work very well: you need to understand how each of them match--in detail--to you, not how they match each other. If you know only their results to each other, you can't determine which lines of the family they may descend from, even if they do both fall into your tree somewhere.

Back to the "hard yards" and then I'll shut up. Autosomal DNA triangulation ain't brain surgery, but it does get more demanding as you move back in time. Working with 2nd cousins is easy; it's like a Bandaid on a scrape. Third cousins take a little investigation, but the complexity has moved only to about a small first-aid kit and some Neosporin and a butterfly closure on a cut. At 4th cousins, you've moved to actual surgery; it may be local anesthesia and an arthroscope, but it ain't easy. By 5th cousins, you're in the full OR with a surgical team, the patient is under general anesthesia, and has signed an "if things go south" consent form. Validating out to 6th cousins is extremely rare; I've seen very few of these that I don't believe could withstand a challenge. At that point, yeah, it sorta is an extended bifrontal craniotomy at the Johns Hopkins Comprehensive Brain Tumor Center.  ;-)

Most of the casual triangulations you see are likely erroneous. I'll add here that on WikiTree the guidelines make it seem as if triangulation applies only to relationships greater than 3rd cousins, that it isn't used for 3C or 2C. Those are local procedural guidelines only, established in order to try to accommodate and explain an otherwise complex process. In fact, autosomal triangulation as a way to accurately assign segments of DNA to an identified shared ancestor or ancestral couple (beyond a generation or two) has never been scientifically studied or verified. While it's recognized anecdotally and empirically as a useful technique, there are zero standards for it.

What makes it so difficult beyond a few generations is that as the amount of shared DNA decreases, the number of possible options for pathways that might explain that sharing increases. It isn't accurate to simply locate two other people who say they descend from the same couple and claim a valid triangulation between, for example, 4th cousins. There has to be an examination of the other possible pathways to rule out that the shared segments didn't come from those pathways.

One of the biggest hiccups here is the previously mentioned pedigree collapse. For example, I've see triangulations where 4th cousins purportedly share 32cM. The theoretical average at 4C is 13.28. There's always variance and wiggle room, but a rule of thumb I use is that if the amount shared is double the theoretical average or more, it's solid evidence of pedigree collapse and that shared segments are most probably traveling across family branches, that the recent family tree is not a rigid ahnentafel structure. So then you have to dig in and look at all the other possible pathways for those shared segments and rule them out before you can accurately make a decision about the most recent ancestral couple.

Another hiccup is the perennial debate over segment size. To go farther than 4th cousins, you have to look below 10cM...but that's risky. As I mentioned, Jim Bartlett can afford to assume a 7cM segment to be valid because he has 20 other individuals in that triangulation group to verify the TG. But from non-peer-reviewed research by John Walden, based on segment analysis using traditional trio phasing on 9,000 haplotypes, looking at a single instance of an 8cM shared segment will turn out to be false 38% of the time; a 7cM segment false 58% of the time; a 6cM segment false 74% of the time; even a 10cM segment will be false about 14% of the time. That's why Jim has a whole bunch of individuals in a TG before he'll trust a smaller segment. (And before I get piled on, by "false" here I mean not of genealogical IBD significance.)

Historically--and where the term was first used with DNA--triangulation with yDNA "required" only you and one other male plus the known MRCA: three points. I personally think it's best done with you plus two other tested individuals: four points, and three legs to the stool. But the Y-37 results are what they are: you and ManB share a paternal ancestor. If you can work out the autosomal evidence accurately and with enough detail, and it properly aligns on your father's side of the equation, I'd say you can take that to the bank. And it would be a huge boost to your genetic analysis of your genealogy.

Scofflaw - I love it - but are you talking about the Chicago Gin Bar or flaunting the WikiTree law ?. On a more serious note, thanks for the detail, but if that is 101, maybe you should start at high school level. I have a B.Sc. in Botany and Zoology, but that was in the mid-60's so its all a bit foggy now. Patronising is good.

A few points if you could clarify please. I have uploaded my FT-DNA data to GEDmatch, which I assume WikiTree links to, rather than having its own database ?. I have not uploaded ANCESTRY results. If I do, do they merge or sit "adjacent" in GEDmatch ?. Do I use the same GEDmatch number to upload ?. Should I also ask A and B to do the same, to make life easier ?. Another clarification; are we looking at just X and Y chromosomes, or do the other 22 get into the genealogy act as well?

Close and distant same surname cuzzies have proved reluctant to test, which really makes it hard to get a baseline. I'm OK with spreadsheets provided I can work out what I'm looking at.. Downloading from GEDmatch to CSV sounds like a good starting point.

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