At what generation does the connection between two individuals first appear or cease to appear?

+5 votes
236 views
For example I am associated with Claunch-23, 66, 26 but not with 318 who happens to be the father of 26.
in Genealogy Help by Ralph Hayes G2G1 (1.7k points)
retagged by Ellen Smith

Where are you NOT seeing the relationship?

When I checked for one, I got:

There is a direct ancestral relationship. Hieronymous Claunch is the great, great, great, great, great, great, great grand father of Ralph Hayes.

Hieronymous is the 7th great grandfather of Ralph

1. Ralph is the son of Twyla (Clonch) Hayes [unknown confidence]
2. Twyla is the daughter of Marlin Preston Clonch [unknown confidence]
3. Preston is the son of Aluvand Clonch [unknown confidence]
4. Aluvand is the son of John William Clonch [unknown confidence]
5. John is the son of William Clonch [unknown confidence]
6. William is the son of Dennis C. (Claunch) Clonch [unknown confidence]
7. Dennis is the son of Jeremiah Claunch [confident]
8. Jeremiah is the son of Jeremiah Claunch [unknown confidence]
9. Jeremiah is the son of Hieronymous Claunch [unknown confidence
This makes Hieronymous the seventh great grandfather of Ralph.

I believe I see the problem. After six generations the autosomal DNA terminates
That is indeed the problem. But it might not be a "problem."

After 7 generations we have less than 1% of the DNA that any specific progenitor 7 generations back had. So the "cut off" is probably intentional & meaningful.

Best!

2 Answers

+16 votes

Hey, Ralph. If you happen to be referring to the panel to the right-hand side of profiles labeled "DNA Connections," that's a mechanism to provide hints about possible shared DNA.

For autosomal DNA, it extends up and down the tree for six eight relationship degrees: horizontally along the tree out to 3rd cousins; and vertically up the tree as far back as a 6th grandparent. The six eight degrees is sound for those 3rd cousins (about 90% of all 3rd cousins will share measurable, detectable atDNA), but the 6g-grandparents is optimistic, because we can only test living or recent generations and at 7th cousins--contemporary descendants of 6g-grandparents--quite literally 98% of them will share no detectable DNA.

The uniparental types of DNA--the Y chromosome and mitochondria--are a different story. Since these can reach back many generations, even thousands of years, WikiTree will show those hints so long as the appropriate lineage, per the profiles in the tree, are unbroken.

Don't know if I'm answering the right question, but there ya go!  smiley

Edited: Correcting a mistake about which I absolutely knew better. sad

by Edison Williams G2G6 Pilot (248k points)
edited by Edison Williams

Apparently that IS what he's referring to, but it's EIGHT "degrees", not six. His Claunch-26 is 8 generations back (therefore included), but Claunch-318 is 9 generations back (therefore NOT included).

Realistically, you have to draw the line somewhere, or you'd have ridiculously long lists of "associated" people, each of whom have little chance of showing a DNA match. WikiTree draws that line at 8, where - yes, the chance of getting a match is somewhere north of 90%.

Seems to me like we could stand to dial that up to 10, though. Even at 50% (or whatever the exact number is) that's decent odds of getting a match - it seems like that would be worth alerting people to. Then we could field questions about "Why don't we match?" Instead of "Why aren't we associated?" wink 

ok, I see, thanks

Yeppers. You're positively correct. I didn't stop to count; just typed. Never a good idea. frown It is eight relationship degrees that WikiTree uses for atDNA.

I've seen so many believe that the "DNA Connections" panel is somehow displaying matches, not just suggested possibilities for research, that I'd sorta hesitate to move it to 10 steps and 4th cousins. So long as as it was made clear that being able to identify a specific 4th cousin was a 50/50 proposition, I think it'd be okay.

But the flip side is using the same distance vertically up the tree for ancestors. I'd personally prefer that to be limited to no more than 6 steps (maybe that's why I unconsciously wrote 6 steps in the answer?), so 4g-grandparents. Implying that relationships beyond 5th cousins have a reasonable chance of being accomplished by triangulation just isn't accurate.

Now to go back and edit the answer so that I haven't caused confusion...

Hello Edison,

Please see https://gcbias.org/2013/11/04/how-much-of-your-genome-do-you-inherit-from-a-particular-ancestor/

and the chart for the likelihood of inheriting zero blocks from an ancestor.  At eight generations there appears to be at least an 80% probability of inheriting at least one block.

Sincerely, Peter

I believe you may have that reversed, Peter. From that post of Coop's:

At eight generations, Coop's graph is showing, approximately and depending upon chromosome, an 80% to 90+% probability that you will inherit zero "blocks" from a particular ancestor. At 1.0 that Y axis would represent a 100% chance that you will inherit no DNA whatsoever from a given ancestor.

You'll note also that Coop doesn't define how much DNA a "block" represents, nor does he try to determine whether or not a block from a distant ancestor--as necessitated by additional generations and additional segmentation during more meiosis events--would be detectable with current technology between you and your contemporary cousin DNA match who is descended from that ancestor.

For pragmatic purposes, I've always preferred the breakdown in this research paper, which took into account the actual microarray genotyping tests we use, by Henn, Hon, Macpherson, et. al.: https://doi.org/10.1371/journal.pone.0034267. The most relevant table is this one:

Hello Edison,

This is the correct chart from Coop:

At 8 generations the probability of inheriting zero blocks of an ancestor's genome is between 10% and 20%.  So the probability of inheriting at least one block is between 80% and 90%.

The chart you selected is for a particular chromosome of an ancestor.

It's funny, but this is kind of a new subject for me, in a way. When I go through every single ancestor in my tree back to great-greats, there's only 3 people referenced under "DNA Connections" in the autosomal section. The one on my mother's side tested with a different company and isn't on GEDmatch (a 3rd cousin, possibly once or twice removed). The two on my father's side are 5th cousins, and both show up on my great-great grandfather's profile.

So I can access more distant relations, if I want, by just clicking on further-back ancestors.

But still, there's a bit of absurdity in being told what modern day people "probably share DNA with" my ancestor who died in 1901.

The bottom line is that it's a pretty decent system, "as is", and people are going to have questions no matter how you set it up. The problem for me is that there are even fewer relatives on HERE for me than there are on even GEDmatch.
Let's "sanity check" that probability. "Back of the envelope" stuff.

Basically, 8 generations back is 6th-great grandparents, of which there are nominally 256.

There's about 3500cM for each parent. Suppose a segment from that many generations back averages something like 10cM. So, somewhere in the neighborhood of 350 segments for each parent; 700 segments total.

So there's something close to three times as many segments as ancestors. Reasonably, you'd expect most to have 2, 3, or 4 segments, but yeah, there might be a few that just miss out altogether. 10%-20% sounds like it might even be too high a number, but it's reasonable to expect it's some low - but not infinitesimal - number. There might be a dozen (or two, or three) out of the 256 who lose this game of "musical chairs".

You gotta figure that you've got an identifiable segment from practically every 5th-great grandparent, though.

Evening, Peter! Sorry for the belated reply. Got an unexpected offer to tour the reconstructed Apollo-era Mission Operations Control Room today before it opens to the public Monday. Awfully darned cool, with detail right down to, at the console stations, ashtrays with pipes sitting in them and 1969 steel RC Cola cans. Amazing we were even able to hit the moon; the Apollo Guidance Computer for Apollo 11, a big upgrade from the previous missions, had a massive 2k of memory and 32k of read-only data storage. Not a typo. surprise

Thanks for including the graph you were referencing. Made things clearer. I do admit, though, that I went to bed last night wondering how we got off on this seeming tangent. Then an "ah hah!" moment after reading Frank's post. It was my failure to connect the dots; it wasn't a tangent at all.

Pointing to the Coop blog post initially threw me. I didn't immediately snap because, well, nobody's 6g-grandparents have ever taken a DNA test.

I believe what you've done, though, is make a strong case for rewriting the text that appears in the "DNA Connections" panel. But I'll close with that.

As we all know, it isn't dates and generations that drive what we see with autosomal DNA diversity and dilution. It's the meiosis that occurs at gametogenesis. For the very reason that WikiTree only shows "DNA Connections" out horizontally on the tree to our 3rd cousins--if we're sitting on their or our profile--whether or not an individual shares an identifiable DNA segment with a distant ancestor is moot, from the standpoint of using DNA for genealogy, unless a current or recent descendant in that biological line has taken a DNA test with whom results can be compared.

A same-distance descendant to your 6th great-grandparents would be your 7th cousin. At that point you aren't looking at Coop's numbers for an eight-generation separation. You're looking at a 16-generation separation because there have been 16 separate instances of conception. Technically, there have been 32 distinct instances of gametogenesis and genetic recombination, arriving at 16 different recombined, diploid genomes.

Coop's graph that you showed tracks only to 15 recombined genomes, and at that point he shows that any likelihood of having a shared "block" of DNA converges on zero.

Experimental, peer-reviewed results, as I linked to in the Henn study, are in general agreement. At that level, after 16 recombined genomes, the study predicts a 98.9% chance that 7th cousins will share no detectable atDNA whatsoever. The expected amount of DNA sharing is shown as a sex-averaged 0.22cM, which is equivalent to 0.0031% of the genome.

I won't dive into other factors, for example that Coop uses 33 as the sex-averaged number of times crossover occurs per conception event, which is about the lowest average of means I've seen (Harvard geneticist David Reich has used a mean of 45 crossovers for the oocyte and 26 for the spermatozoa for an average of 35.5; using the MLH1 DNA mismatch repair protein as a marker, Gruhn, et. al., arrived at a mean of 69.25 for females and 49.09 for males). Because, yeah, though just some quick and dirty math, I think Coop's numbers are quite reasonable.

Bringing me back to the "DNA Connections" panel. The first description under the "DNA Connections" panel reads: "It may be possible to confirm family relationships by comparing test results with [name] or other carriers of his ancestors' Y-chromosome or mitochondrial DNA." (Remove reference to the Y chromosome and change "him" to "her" for profiles of women.) Then in almost the same breath: "It is likely that these autosomal DNA test-takers will share DNA with [name]." Which is in reference to whatever profile we're viewing, even if someone born in the mid-18th century.

Aren't we implicitly conflating two very different things? We talk about uniparental DNA, yDNA and mtDNA, as a tool by which "it may be possible to confirm family relationships by comparing test results." Which is point-on relevant because genealogists are interested in compiling evidence. But then we shift gears and abandon the "it may be possible...by comparing" to make the relatively pointless statement that someone's 6th great-grandmother might have passed down some tiny segment of atDNA to a list of people who may also be descended from the same person...who was likely born between 1740 and 1800.

Why do we word it that way? I wonder if we could get a show of hands to determine how many WikiTreers believe those lists of autosomal test-takers are intended to provide clues as to whom they might want to research for a DNA match? (Or, a corollary, how many feel those lists actually denote a DNA match?)

I have no idea how the WikiTree algorithm is constructed or how/if it might be modified. We're careful to make 3rd cousins a working atDNA threshold for a couple of different things, "DNA Connections" and autosomal triangulation included, but then we show names under the "DNA Connections" panel that for autosomal DNA--by Coop's numbers, the Henn study, and others--would be as far removed as 7th cousins and 16 recombined genomes, and have a 99% chance of sharing zero detectable DNA. Is that more likely to be useful or misleading to the average WikiTreer? Shouldn't we at least change the explanatory text to make it unambiguously clear that distant relationships have a high probability of yielding no autosomal DNA evidence?

To quote Frank: "But still, there's a bit of absurdity in being told what modern day people 'probably share DNA with' my ancestor who died in 1901." Or in many cases, who died much earlier. A 40-year-old test taker's 6g-grandparents, assuming a conservative 25 years per generation, would have been born in 1804.

But I'm back on track now, thanks. I've matched up the exact text under the "DNA Connections" panel to reality.

Edison, having pondered this a bit more, I think perhaps we're just looking at it the wrong way and I'm not sure if it's our own preconceptions, or the way it's written that got us off course.

When it says that certain test-takers likely share DNA with the subject of a profile, that's just literally true, and it's BECAUSE of that 8 generation policy (that I complained maybe should be 10). When we hear "two people likely share DNA" we immediately jump to thinking about comparing their DNA tests - an absurdity, for many profiles - but that's in our OWN heads. That's not what it's for.

Let's turn your own statistic around! Suppose you wanted a list of people who had any sort of decent chance of matching you. That's exactly the list you'd want, right? At the extreme, the LEAST likely person to match you on that list has about a 1% chance! If we went any further than the 8, people would be included who had a downright remote chance of matching you (not just a small chance).

And yet that list is the same list for everybody! It's not a list that is specifically tailored to the person viewing it. It really works out quite well!

If you look on your OWN list, it would have people out to your 3rd cousins, or equivalent - exactly the people you'd have a 90%+ chance of matching. Yet - again - even THAT list is not drawn up specifically because YOU'RE looking at it - it would be the same list if anybody looked at your profile.

For an ANCESTOR'S list, you're seeing everybody here on WikiTree who has tested, and - like you - has a really good chance of having at least SOME DNA from that ancestor. That doesn't guarantee that they have the SAME segment(s) that you have, but it eliminates the millions of people who have almost NO chance of matching you.

So you just have to look at the list differently, depending on whether it's your OWN profile (where matching them is very likely) or whether it's an ANCESTOR'S profile, where the likelihood drops, the further back an ancestor they are.

Anyway, I'm suddenly a FAN of the 8 generation steps policy, and now think it's pretty slick, the way the whole thing works. I'm glad we did this little exercise. Is there a different way they can phrase things, to interrupt our preconceptions, and get us on track? I dunno!
+4 votes
On Ancestry.com, my Father's DNA is being matched with ancestors living as many as 7 generations previous.  That is based on as little as 6 cM of a single segment.

These types of deep matches are of course dependent on both people having accurate family trees.

Ancestry.com has the ability to spot common ancestors that are not on your tree as long as you do have some ancestors identified within a generation or 2 of the other person's tree.

It's impressive!
by Andrew Ross G2G6 Mach 2 (23.1k points)
There will always be the nay-sayers on that, of course.

In my case, these "deep matches" focus mostly on a pair of 6th-grandparents. I took it with the proverbial "grain of salt" until I discovered that two of the matches were second cousins to each other, the common ancestor being exactly the one that leads towards me. That's not quite enough for a real triangulation, but enough to make me strongly suspect that it's real.

Then I have a match where the MACRs are the parents of that 6th-great grandmother (so, 7th-gt grandparents). They don't match the other guys, so I'll just call that one "interesting", because of those other matches. Maybe I can get some of these folks on GEDmatch someday.

Anyway, it looks like it might have a decent track record, from what I'm seeing.

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