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  #1  
Old 11th February 2017, 07:50 AM
Bingowings Bingowings is offline
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How many mutations are too many?

Hi

My first post here. I've been the admin for a one name project [RID(E)OUT] for some time now; my members ask questions from time to time and I do my best to help them but I'm stumped with this one... can you help please?

I have three members who, on paper, descend from three different sons of 'John' (b. 1745)... the men are five or six generations down from 'John' - two have identical sequences (37 markers), one has 1 fast mutation [DYS458].

Now, a fourth man has joined the project; on paper, he believes himself to descend from a fourth son of 'John' yet, in just seven generations to the CMA, his line shows 3 mutations [DYS460, DYS464c, DYS576] all of which are, I believe, 'fast' - but is this number feasible over so few generations? Is it more likely that the man actually belongs elsewhere on the tree - or is this rate of mutation ever observed?

Cheers, Karen
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  #2  
Old 11th February 2017, 10:41 AM
John McCoy John McCoy is offline
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The difficulty is that there is no way to be sure that the fourth man was simply very lucky and that unlikely mutations actually happened in his lineage. What is needed here is a sense of exactly how unlikely this outcome is.

Another way to proceed would be Big Y or a similar SNP-based analysis. If the first three samples do in fact belong on the same twig of the haplotree, as determined by careful analysis of Big Y or other SNP analysis, and if the fourth sample doesn't belong on that twig or one of its twiglets, then you would have evidence pointing to a different origin. Or, if it does cluster with the others, then you have evidence that he has a similar origin, not necessarily with the common ancestor shown by the paper trail, but at least from a close patrilineal relative.

Also, the statistical context might be more persuasive if it turns out that the surname has many different, genetically distinct origins. If, on the other hand, the genetic evidence points to most or all such families having genetically similar origins, it becomes much harder to argue that one of them is different from the others.

I have a feeling the genetic evidence may be able to rule out some possibilities, but it may not be powerful enough to distinguish ancestral brothers from other patrilineal relatives.
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  #3  
Old 11th February 2017, 11:03 AM
Bingowings Bingowings is offline
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Post How many mutations are too many?

Hi John

Thank you for your very prompt and helpful response.

Your first sentence encapsulates my problem... 'what is needed here is a sense of exactly how unlikely this outcome is' and that is what I don't have. I have to admit that I do find that the statistical elements of some of these analyses a bit baffling; one can find mutation rates for individual markers but not the likelihood of three mutations occurring within one time period (7 gens, ~170yrs). I haven't looked into Big Y so I'll need to do some reading but, all supposing that it involves further testing, I'm not sure that all four of my members would be interested, particularly since three of them are comfortable that they know their lineage. Still, I will do a bit of research: I'm very grateful for your input so thank you again

Cheers, Karen
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  #4  
Old 11th February 2017, 03:43 PM
John McCoy John McCoy is offline
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The most basic approach is to consider the 3 mutations as independent events, and compute the probability that all three sites mutated within the known number of generations. However, there are some cases where a whole stretch of the Y chromosome, containing several nearby STR's, has apparently undergone some sort of major reorganization, all at once. In other words, mutations of STR's may not always be independent events. Another complication that can't easily be measured is that there is no reason to suppose that every Y chromosome experiences the same mutation rate. A lot of unknowns!
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  #5  
Old 11th February 2017, 03:54 PM
Armando Armando is offline
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Quote:
Originally Posted by Bingowings View Post
Your first sentence encapsulates my problem... 'what is needed here is a sense of exactly how unlikely this outcome is' and that is what I don't have.
For an example of a large GD in a few generations see Prairielad's post where he says..
Quote:
Originally Posted by prairielad View Post
My father and his paternal 1st cousin are 4GD at the 37 and 67 marker level.

My Uncle and same cousin are 3GD @ 37 markers

My father and his brother are 1 GD @ 37 markers. Difference is my father registers a 2 step at DYS576 and my Uncle has only a 1 step.
Quote:
Originally Posted by Bingowings View Post
I haven't looked into Big Y so I'll need to do some reading but, all supposing that it involves further testing, I'm not sure that all four of my members would be interested, particularly since three of them are comfortable that they know their lineage. Still, I will do a bit of research:
The BigY does involve further testing and it is expensive but it tests SNPs which can be much more reliable and SNPs can be dated since new SNPs happen about every 3-4 generations. You can see video where STR matches and BigY tests were used on a lot of people that matches at 67 markers at https://youtu.be/pxexkvfus6w proving that BigY helps determine how closely people are related to within about 100 years. It takes a $49 YFull analysis to get a TMRCA of the SNPs so you have to tack on that price to the BigY testing to understand how expensive it all is.
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  #6  
Old 12th February 2017, 06:04 AM
Jim Barrett Jim Barrett is offline
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Quote:
Originally Posted by Bingowings View Post
Hi

My first post here. I've been the admin for a one name project [RID(E)OUT] for some time now; my members ask questions from time to time and I do my best to help them but I'm stumped with this one... can you help please?

I have three members who, on paper, descend from three different sons of 'John' (b. 1745)... the men are five or six generations down from 'John' - two have identical sequences (37 markers), one has 1 fast mutation [DYS458].

Now, a fourth man has joined the project; on paper, he believes himself to descend from a fourth son of 'John' yet, in just seven generations to the CMA, his line shows 3 mutations [DYS460, DYS464c, DYS576] all of which are, I believe, 'fast' - but is this number feasible over so few generations? Is it more likely that the man actually belongs elsewhere on the tree - or is this rate of mutation ever observed?

Cheers, Karen
Do you have a public website for the project? If you do and if you'll provide the kit numbers for the four people we can view the results and perhaps make better suggestions.
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  #7  
Old 14th February 2017, 09:52 AM
Bingowings Bingowings is offline
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How many mutations are too many?

Hi... in answer to your question, no we do not have a public website. However...

Males 3, 4, 5 & 6 have 37 markers identical and an established CMA 6-7 generations back. Male 1 also has documentary evidence of belonging to this family and shares a closer relative with two others and so he has a single mutation (DYS458) in his own line. The chap (Male 2) who believes himself part of this group, on paper, is 7 generations down from the CMA but has 3 mutations as shown above. My original question was: is he likely to be related to this group or not based on the DNA results alone? The situation is 'difficult' as he is adopted but is in touch with his birth father, who passed on the genealogical information to him, much of which has documentary evidence.

Thanks for looking at this; I would be very glad to have some opinions :-)

Regards
Karen
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  #8  
Old 14th February 2017, 05:02 PM
The_Contemplator The_Contemplator is offline
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As Armando has shown with examples, a GD of 3 at Y37 can still mean they are from the same lineage. I have seen that in some kits I manage. Same surname and paper trail leading to a common ancestor from the late 1500's through different sons. Some don't even show up as Y37 matches due to having a GD greater than 4.

Of course there are matches that could be NPEs with the same genetic distance. SNP testing through a NGS test like Big Y will remove any doubt.

Two of the 3 markers you listed are labeled as fast mutating by FTDNA. If you look in a project's results page, the markers are labeled at the top. The ones in red have been determined by FTDNA to mutate more frequently.

Based on what you have said, it looks good.
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  #9  
Old 15th February 2017, 08:41 AM
Bingowings Bingowings is offline
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The_Contemplator

Thank you very much; I don't think I had realised how much variability there could be in the data! I draw the conclusion that these yDNA tests are almost like paternity tests... they can't prove that you are related but they can prove that you're not... except now the answer is 'you might be' :-)

Cheers
Karen
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  #10  
Old 16th February 2017, 09:07 PM
benowicz benowicz is offline
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Generations Probability Cumulative
1 0.001317 0.001
2 0.007626 0.009
3 0.018626 0.028
4 0.031953 0.060
5 0.045167 0.105
6 0.056488 0.161
7 0.064923 0.226
8 0.070142 0.296
9 0.072285 0.369
10 0.071770 0.440
11 0.069144 0.509
12 0.064976 0.574
13 0.059798 0.634
14 0.054062 0.688
15 0.048133 0.736
16 0.042286 0.779
17 0.036716 0.815
18 0.031551 0.847
19 0.026863 0.874
20 0.022682 0.897

Using the 30 year generation convention, they're probably all around 6 gen. out from the common ancestor. So roughly 16% percent chance. Not encouraging, but not out of the question.

http://clandonalddnaproject.org/inde...rca-calculator
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