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General => Ancestral Family Tree DNA Testing => Topic started by: jon541 on Friday 07 March 25 18:18 GMT (UK)
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I have a new match on Ancestry against my mother's test which I was interested in because it shows a shared match with someone descended from an ancestor with a surname that has been a problem for me, said ancestor hailing from the same tiny Northumberland hamlet as "my lot". Only 9cM/1 segment but hey... Ancestry say that this match is on my mother's maternal side which would be correct if there is indeed a link.
But when I check the same Ancestry member against my own test, it comes back as 15cM/2 segments and the maternal/paternal attribution is given as "Unassigned".
My question is: how is that even possible or do you think it's a mistake? The only way I can think of that I could have a stronger DNA match than my mother is if I also have a segment match against this person inherited from my father. I've occasionally seen a one or two cM increase which I've put down to the sampling science not being 100% correct but this is much more marked.
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I think your deduction is plausible at such small cm amounts there can be variations between generations matches .
Most of my own unassignded cases have no trees or unlinked trees .
I'm lucky because I can check if they match my mother my paternal aunt's cousins from both sides and a nephew.
Sometimes I'm surprised by the amounts and as my parents have very different origins crossovers are unlikely but I did once find a match to descendant of Scottish Canadian lumberjack who'd married a descendants of a Latvian Jewish person so I matched on both sides .!
Tiny amounts
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My polish friend is building a tree he has mostly distant matches ..top one is unassigned .
His parental DNA show similar ethnicity amounts .
I expect there will be cross over somewhere
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In the science of Mathematics there is an area called Fuzzy Logic.
In the world of Ancestry there is “Fishy Logic”!
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Very funny Biggles.
Fortunately, I have a little more faith than that despite the example I gave looking a little 'fishy'.
Where you really have to be careful is with Thrulines... potentially a brick-wall demolisher but because it is dependent on other people's trees (many of which as we all know are dodgy / based on supposition not backed by solid research / based on wild flights of fancy) sometimes the suggested connection with a DNA match can be way off the mark.
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Granted this is an MH screengrab so not a direct comparison and these are much larger matches than those in the original query. There's quite a marked difference here considering it's comparing a parent (Dan), and child (Alfie), to a 3rd party(me).Chromo 12 is pretty obvious but on chr21 the segment to Alfie is twice the size of that to Dan.
I share 320cM with Dan across 16 segments and 286 to Alfie across 12 on MH, On Ancestry it's 319 across 16 to Dan and 280 across 11 to Alfie. In some ways my DNA is more like Alfie's than it is to his dad although his dad is a generation closer to me and a larger total share. In fact for the relationship I have with Alfie we are above the limit using shared cM tool as it's a '† this relationship has a non-zero probability for 280cM in thednageek's table of probabilities, but is outside the bounds of the shared cM project (99th percentile)' example
Alfie's mum has tested and there's no match at all with me and the Ancestry results show no odd/stray matches to Alfie that Dan doesn't have so I'm pretty confident I only link to Alfie through his dad.
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But when I check the same Ancestry member against my own test, it comes back as 15cM/2 segments and the maternal/paternal attribution is given as "Unassigned".
This is something I've noticed. Biggles may be able to ad a bit more on the science, because I am not that well read on it.
That is, you have two DNA matches (child and parent) and the child has more shared DNA than the parent.
The first aspect to understand is on the inheritance of DNA, which is random, within certain limits and aligning with certain norms. We inherit a random mix of DNA from each parent, with a segment from one and a segment from the other. I believe that the average size of an inherited segment is about 20cM, but can theoretically be an entire chromosome. Where I've noted these matches where a child has a larger share of cM to you than the parent is with matches under 30cM. So it's in this area where there is quite a high chance of inheriting a full chunk from a parent that represents a full chunk inheriting from a grandparent.
As you probably know Ancestry has their Timber system to strip out shared cM that it thinks are coincidental (rather than inherited by descent). It seems the most likely cause of these cases is that for some reason Timber doesn't recognise the so much of the shared cM as coincidental. Maybe the adjoining portion of DNA, inherited from both or the other parent happens to be identical by chance. Ancestry tries to strip those out, but maybe can't all the time.
The other possible answer is that you have extra shared DNA from the child's other parent. In my experience I'd say Ancestry's maternal, paternal, both guides for DNA matches in the range of about 30cm+ are close to 100% accurate. But below that it's more likely to get into "unknowns" and assigning people to the wrong side. When this is the case, I find that it's liable to assign many of the matches of a line on the wrong side. Below 30cM the unknowns mount up and it's probably less than 90% accurate with smaller matches of around 8-12cM.
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On the 9cM match, from what I have seen these have the possibility of being quite deep. I have absolutely certain clusters going back to around the 1650s-1660s on a few lines. In a couple of them, there are matches from child, parent, grandparent, with low cM in the range of 10cM. And the child, parent and grandparent all have roughly the same shared cM.
This relates to the above, where the average inherited size of a segment is around 20cM. The smaller the segment the more likely it is to be inherited over multiple generations at exactly or roughly the same size. There's also regions of DNA that are more or less likely to be split. So when you have matches that show common ancestry going back to the 1600s, they are probably from those regions.
So, what is the maximum number of generations one can inherit these small segments? Certainly to 8th cousins, but presumably more.
But there's also the question of whether a 9cM match on Ancestry may be a false positive. I think there are no to few false positives >= 40cM, 30-30cM - maybe a small amount, 20-29cM - maybe more, 15-19cM - maybe more, 10-14cM - maybe more; and so on. Hard to say. The largest match I have that may be a false positive is 43cM. I have a few clusters of DNA matches where the largest match is in the 20-30cM range. These are always huge clusters with 100s of matches, and the common ancestry always goes back to the Carolinas in the US. I don't know what to make of that. The genealogical record of the Carolinas seems to be poor, with very mixed, jumbled, unsourced and abominable public trees. With clusters where the common ancestry is in the US, it's possible that there was an immigrant ancestor and people have just botched in any old US line, as there's probably no record of place of birth. So maybe those clusters are just muddled, but the size of them suggests that they may be false positives. Since Timber is meant to strip out commonly occurring parts of DNA; and these are very large clusters at lower cM.
When I have matches that are isolated, without other shared matches who share the same ancestry, I note that and don't consider it proof like I would if they were in a cluster with 10 other people who have shared ancestry. In such cases more tests might help. Much more tests in the case of 9cM matches.
I have a line of ancestry from Fife, starting in 1794, with no other ancestry in the area. In my aunts/uncle's DNA tests I found two clusters of matches going back to that area, but with 23cM being the largest shared, few matches and not many with determinable shared ancestry. Recently I got hold of a half 4th cousin's DNA test (who was not a match of my relatives) and he had a few of these shared matches in common, and then other matches. So this had led me to put it down as genetic proof. I was a little cautions to seal it as there are two generations where there are no matches and then a faint cluster. Whereas if you have a lot of matches, you can often link one generation into another into another.
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To add to that. When I've found this phenomena of a child having more shared DNA than a parent, it's usually 1-2cM more. The largest is about 5cM extra for the child, on larger matches, maybe 24 + 29.
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To add to that. When I've found this phenomena of a child having more shared DNA than a parent, it's usually 1-2cM more. The largest is about 5cM extra for the child, on larger matches, maybe 24 + 29.
That's what I've noticed too, it's much more prevalent with the smaller matches and does seem to appear more frequently with matches from the USA but perhaps that's down to dna uptake being greater there than the UK and a higher chance that several people in a family have tested. I have the odd 3 generation UK batch here and there (child/parent/grandparent), but the US equivalent will be five kids, their parents and all four grandparents plus an assortment of cousins, aunts and uncles thrown in for good measure. They are the type that when I view them in protools everyone seems to share upwards of 500cM to everyone else in the list but are all just 20-25cM to me and the younger generations can often be the same or 1-2cM higher than an older generation.
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Veering wildly off topic now but another trend I've noticed is many UK matches who were born in the 1940's, if they have trees they are generally just two or three generations deep and often have no paternal side. Few have profile information but I do wonder if many of them are wartime babies trying to find the identity of their father. Coupled with what seems to be an increasing number born in the swinging 60's who are trying to find an unknown grandfather it seems like two generations seeking the answer to the same question.
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Glen don't forget the test tube sperm donor babies ! I have a match with one of them .
Re the child having higher match than parent I managed 3 generations of tests and have come across it before I will look for some concrete examples
Where my nephew has higher amounts than me I assume his mother had stronger amounts from 1 ancestor
If I'm higher than my paternal aunt I assume the distribution of ethnicity varied between her and my father
But if it's myself and my.mother it's harder to explain
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I've just found a paternal match.whom I match by 109cm
Match is 's 49cm to my aunt 47cm to my nephew
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Veering wildly off topic now but another trend I've noticed is many UK matches who were born in the 1940's, if they have trees they are generally just two or three generations deep and often have no paternal side. Few have profile information but I do wonder if many of them are wartime babies trying to find the identity of their father. Coupled with what seems to be an increasing number born in the swinging 60's who are trying to find an unknown grandfather it seems like two generations seeking the answer to the same question.
That very subject is what the BBC Sounds series The Promise is all about.
I have listened to it and it really shows just how easily the wrong path can be taken in genealogy research.
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Veering wildly off topic now but another trend I've noticed is many UK matches who were born in the 1940's, if they have trees they are generally just two or three generations deep and often have no paternal side. Few have profile information but I do wonder if many of them are wartime babies trying to find the identity of their father. Coupled with what seems to be an increasing number born in the swinging 60's who are trying to find an unknown grandfather it seems like two generations seeking the answer to the same question.
That very subject is what the BBC Sounds series The Promise is all about.
I have listened to it and it really shows just how easily the wrong path can be taken in genealogy research.
Melding the original topic in with my off topic bit I have a match that came up the other day who is looking for a missing grandparent and detailed on her profile though it's not a wartime period case. She matches three descendants of my grandmother who are in 3 different generations but doesn't match the 5 others who have tested in the same 3 generations. She matches a child but not their parent, the biggest match is a middle generation and the middle match is the highest generation. Everything seems back to front apart from the link being her maternal side. I'm tempted to say we just fall the wrong side of the 3c line but it's got me scratching my head every time I look at it.
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re reply 9
my mother has several matches to children and grand children of her known SMITH 2nd cousins
over 5 years I have worked out who most of them are including 3 with no trees + 2 who didnt know their fathers .its very interesting to see how they
match each other +3 generations of JONES 2nd cousins
identification of who's who was helped as the 5 second cousins had from same father had 2 different mothers
i will do a case study on this forum ...
im lucky that so many elders born between 1930 + 1945 have tested ..including 1 war baby .. a product of a twin so their top match is either a half sister or cousin
most of the others can be confirmed by matches to their neices/nephews or half cousins
or full siblings ( very useful when protools indicates that a Smith with just a first name no age or location is the brother of someone that i do know )
that leaves a high match +her son whose unusual surname has intrigued me after yesterdays success identifying the father of a 90 year old i think i can calculate her parentage too .
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Veering wildly off topic now but another trend I've noticed is many UK matches who were born in the 1940's, if they have trees they are generally just two or three generations deep and often have no paternal side. Few have profile information but I do wonder if many of them are wartime babies trying to find the identity of their father. Coupled with what seems to be an increasing number born in the swinging 60's who are trying to find an unknown grandfather it seems like two generations seeking the answer to the same question.
I plead partly guilty to the above. My online tree is purely my maternal side (although somewhat more than 2-3 generations) because my 2021 DNA test demolished my 75 year long presumption that I knew who my biological father was. I now have a very large research tree based on my biological paternal matches but still cannot place myself in it, so remain unable to add it to my DNA result. After the bombshell I stopped work completely on what I had previously thought was my paternal side (and had spent around 17 years assembling). I also spend little time thinking about expanding my maternal side even though I now have over 14,000 maternal matches on Ancestry alone. I suspect that people like me are reluctant to go too public in their profiles for fear of putting off prospective close relatives.
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Veering wildly off topic now but another trend I've noticed is many UK matches who were born in the 1940's, if they have trees they are generally just two or three generations deep and often have no paternal side. Few have profile information but I do wonder if many of them are wartime babies trying to find the identity of their father. Coupled with what seems to be an increasing number born in the swinging 60's who are trying to find an unknown grandfather it seems like two generations seeking the answer to the same question.
I plead partly guilty to the above. My online tree is purely my maternal side (although somewhat more than 2-3 generations) because my 2021 DNA test demolished my 75 year long presumption that I knew who my biological father was. I now have a very large research tree based on my biological paternal matches but still cannot place myself in it, so remain unable to add it to my DNA result. After the bombshell I stopped work completely on what I had previously thought was my paternal side (and had spent around 17 years assembling). I also spend little time thinking about expanding my maternal side even though I now have over 14,000 maternal matches on Ancestry alone. I suspect that people like me are reluctant to go too public in their profiles for fear of putting off prospective close relatives.
Bite the Bullet.
You are not alone as there are quite a few here in exactly the same situation as you.
Me included.
Last year I held my Half Sister in my arms for the first time.
It required Detective work and speculative contacts with people who had not taken a DNA test but it paid off.
When I walked up the path to her door and we saw each other there was no doubt we were family. She took a DNA test for me and we have been seeing each other regularly ever since, we were recently at the family gathering for my new Brother in Law’s milestone birthday and we are meeting up again this Friday. We only live a 45 minute drive away from each other.
I now know who my bio Father was and all about what he was like as a person.
So when you feel ready, start a new thread and tell your tale.
We can help.
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Thanks to all for the interesting, thought-provoking and heart-warming (Biggles) answers to my original query.
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Re the original question and particularly the Dan Alfie
I came across a case a few years ago which could be another possibility.
" A father and son " on paper were actually brothers elder brother bringing up a younger "surprise" baby
With 2 brothers there can be one has inherited part of the jumble that makes up your DNA
Does that just give sotmethng else to think about
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The Ancestry to Ancestry tests for Dan and Alfie show 3488 cM share. Their MH to MH show 3534 cM
Dan's uncle has also tested but just on MH, the share with Dan on there is 1537 and 855 with Alfie.